pH Meter Calibration

[schematix]

Long time brun'water user, first time pH meter user.

A bit over a year ago i got a Hanna 98128 meter along with storage solution, and 4.01 and 7.01 buffers. Everything has been unopened/sealed and kept cool/dark since i got it.

Yesterday (>24h ago now) i took the meter out, rinsed it off, and then filled the cap with storage solution to rehydrate the sensor. This morning i changed the solution and let it sit for another 6h or so.

Just now I poured myself about 50-75mL each of the buffers and i've been trying to run the calibration procedure. When i do this it first asks for the 7.01 buffer, and about a minute later accepts in and then asks for the 4.01 buffer. About another minute later it accepts the full 2-pt calibration. Now as the meter sits in the 4.01 buffer the measurement drifts down to 3.94 over the course of a few minutes. If i clean it/rinse it and take it back to the 7.01 buffer i'm reading about 7.03 after several minutes. If i clean/rinse and go back to the 4.01 buffer its reading 3.94 again.

If i do single point calibrations after its been sitting for several minutes it measures exactly the buffer value, but the other buffer measures off by almost 0.1

I would have expected no more than +/- 0.01 readings from 4.01/7.01 going back and forth between the buffers since it was just calibrated in them.

Any idea what is going on here?

 

[day_trippr]

@ajdelange noted a potential issue with calibrating the 98128 here
https://www.homebrewtalk.com/showpost.php?p=6690674&postcount=4

Also, his epic calibration thread is worth the read...
https://www.homebrewtalk.com/showthread.php?t=302256

Cheers!

 

[schematix]

Unfortunately i became aware of that 'flaw' about a week after i got it.

I'm already thinking this thing is destined for the scrap pile.

 

[mbobhat]

Yesterday (>24h ago now) i took the meter out, rinsed it off, and then filled the cap with storage solution to rehydrate the sensor. This morning i changed the solution and let it sit for another 6h or so.

If the probe was dry all this time you may have screwed up the probe. I would let it sit in the storage solution and see again in a week or so.

 

[schematix]

If the probe was dry all this time you may have screwed up the probe. I would let it sit in the storage solution and see again in a week or so.

I have to imagine these are somewhat tolerant of being dry because who knows how long it'll be from the time its bought until the time its actually used the first time... but i could be wrong. I'll check with Hanna and see what they say.

 

[Hanna_Brewing]

Hi @Schematix, and guys,

I'm glad you brought that up!

So the reason you are seeing that change of +/-0.04 pH is not because the meter isn't reading correctly but because LITERALLY the pH in your buffer has changed.

So things like oxygen and temperature (heating or cooling) will actually change the pH of a solutions. Granted usually this change is minimal (i.e. +/- 0.05 pH) in a short amount of time or at a small temperature change from 25 Degrees Celsius. So the buffers are meant to report their value (4.01/7.01) at 25 degrees Celsius but if they are not at that exact temperature (which of course it won't always be) the actual value of your buffer is different. Now because you are using the HI98128 which has ATC (Automatic temperature Compensation), your meter knows the relation between temperature and pH to account for that difference when it calibrates.

 

[schematix]

Hi @Schematix, and guys,

I'm glad you brought that up!

So the reason you are seeing that change of +/-0.04 pH is not because the meter isn't reading correctly but because LITERALLY the pH in your buffer has changed.

So things like oxygen and temperature (heating or cooling) will actually change the pH of a solutions. Granted usually this change is minimal (i.e. +/- 0.05 pH) in a short amount of time or at a small temperature change from 25 Degrees Celsius. So the buffers are meant to report their value (4.01/7.01) at 25 degrees Celsius but if they are not at that exact temperature (which of course it won't always be) the actual value of your buffer is different. Now because you are using the HI98128 which has ATC (Automatic temperature Compensation), your meter knows the relation between temperature and pH to account for that difference when it calibrates.

Is the calibration routine also compensating for how it expects the buffer to change pH with respect to temperature, in addition to the probes reaction?

How long is a buffer accurate for after being opened, or poured from a bottle?

I'm having trouble rationalizing how the pH dropped that much right after calibration. According to a correction table i'm finding for 4 buffer, it should have still been around 4.00 at the temperature it was at (about 66F).

 

[mbobhat]

Another thing, if the buffer is varying by that much, try measuring an actual sample, like tap water with some vinegar in it, and see how much it drifts...that will tell you whether your probe is crap or not. Keep the temp the same each time and you'll see if it will work for brewing or not.

 

[ajdelange]

So the reason you are seeing that change of +/-0.04 pH is not because the meter isn't reading correctly but because LITERALLY the pH in your buffer has changed.

No, it isn't. As has been noted earlier in this thread the problem with this particular meter is that it accepts calibration readings as being stable before they really are. The electrode in the unit I tested was actually quite stable (stability checks must be done at constant temperature - see the sticky referenced in #2) and the meter can be used successfully in brewing simply by determining how far off it is in 4.0 buffer after cal and applying that offset to readings.

This is a design flaw. The user should be the one who determines when readings are acceptable - not the meter. It's fine to have automatic stability detection but the user should be able to override it.

Buffer pH does change with temperature which is why one holds buffer temp when doing a stability check. The only thing in air that's going to stress a buffer is CO2 and there is so little of that that the influence on 4 and 7 buffers is negligable. The effect on 10 buffer (which is a carbonate buffer) is not negligable and this buffer must be protected from air.

Now while we know this meter to be subject to this problem the magnitude of the drifts are larger than we would expect to see from this effect. i'd continue to soak this electrode for a few days and then run the stability check again.

 

[ajdelange]

Is the calibration routine also compensating for how it expects the buffer to change pH with respect to temperature, in addition to the probes reaction?

Absolutely! Or at least it had better be. The meter assumes that you are using NIST traceable operational buffers and their pH vs temperature curve is programmed into meters. One representation of that data is given in the calibration sticky referred to in #2.

How long is a buffer accurate for after being opened, or poured from a bottle?

Certainly several hours with the possible exception of pH 10.

I'm having trouble rationalizing how the pH dropped that much right after calibration. According to a correction table i'm finding for 4 buffer, it should have still been around 4.00 at the temperature it was at (about 66F).

As I noted in my previous post that does seem a lot.

 

[ajdelange]

Another thing, if the buffer is varying by that much, try measuring an actual sample, like tap water with some vinegar in it, and see how much it drifts...that will tell you whether your probe is crap or not. Keep the temp the same each time and you'll see if it will work for brewing or not.

No. Do it with the buffers. They don't change in pH over time. They do change with temperature but they change less with temperature than solutions of acid. Also buffers have high buffering capacity at their design pH's. Vinegar, for example, does not. This means that the buffer will resist pH change from external stress better than vinegar will. That's why we calibrate with buffers rather than with just acid.

 

[day_trippr]

fwiw, I've noticed my 98128 taking longer and longer to reach a stable reading.
But as I use Bru'n Water the testing is generally confirmatory in nature.
So it hasn't been a big deal to wait it out.

Otoh, it's pretty much non calibratable at this point.
I tried a 2-buffer cal and for sure it never got a proper 4.01 reading before it called for the 7.01 - which it almost certainly couldn't have gotten right, either.

So...here's a question: is there a dry shelf-life for this type of pH probe?
Meaning, from its build date to date of first use, can a probe time-out before it's even sold?

Cheers!

 

[ajdelange]

I'm sure there is, as with many things but it ought to be better than a year. pH meters of this type contain two or more chambers filled with fluid or gel. One or two of them are completely sealed but at least one is open to the outside. This will eventually dry out even in packaging but that should take at least a couple of years I'd think.

 

[Hanna_Brewing]

Is the calibration routine also compensating for how it expects the buffer to change pH with respect to temperature, in addition to the probes reaction?

Absolutely the meter is adjusting for this.

How long is a buffer accurate for after being opened, or poured from a bottle?

Buffer 10 is less shelf stable then buffer 4 once it has been opened. As a rule of thumb we say it'll last 6 months from when you first opened it.

I'm having trouble rationalizing how the pH dropped that much right after calibration. According to a correction table i'm finding for 4 buffer, it should have still been around 4.00 at the temperature it was at (about 66F).

You probe could need further hydration, the junction may need to be refreshed or the probe may need to be cleaned. I wouldn't recommend wiping the bulb. Just clean it with a cleaning solution. Ideally the proteins cleaning solution works best to break down proteins from beer. You could try this as well for Kombucha. Otherwise, you can try a simple general purpose cleaning solution. Also, you should clear your previous calibrations before calibrating again.

The pH testers have a very specific window in which they will accept a calibration. If the reading isn't stable the meter will not accept and move on. If you'd like, I can calculate your Slope and Offset to asses the quality of your probe. Theoretically your Offset should be 0 mV. An acceptable window is +/- 30mV which is programmed into the meter. Your slope should be between 85-110%. As long as a probe is within these specs it's a good probe. Although your meter technically doesn't show this there is a way to figure it out:

Go into Calibration mode and clear your calibration. Then, without calibrating, go back to measurement mode. Take a reading of your 7.01 pH Buffer and write down your result,. Then take a reading of your 4.01 Buffer and write that result down. Let me know what your meter reads.

 

[schematix]

Absolutely the meter is adjusting for this.



Buffer 10 is less shelf stable then buffer 4 once it has been opened. As a rule of thumb we say it'll last 6 months from when you first opened it.



You probe could need further hydration, the junction may need to be refreshed or the probe may need to be cleaned. I wouldn't recommend wiping the bulb. Just clean it with a cleaning solution. Ideally the proteins cleaning solution works best to break down proteins from beer. You could try this as well for Kombucha. Otherwise, you can try a simple general purpose cleaning solution. Also, you should clear your previous calibrations before calibrating again.

The pH testers have a very specific window in which they will accept a calibration. If the reading isn't stable the meter will not accept and move on. If you'd like, I can calculate your Slope and Offset to asses the quality of your probe. Theoretically your Offset should be 0 mV. An acceptable window is +/- 30mV which is programmed into the meter. Your slope should be between 85-110%. As long as a probe is within these specs it's a good probe. Although your meter technically doesn't show this there is a way to figure it out:

Go into Calibration mode and clear your calibration. Then, without calibrating, go back to measurement mode. Take a reading of your 7.01 pH Buffer and write down your result,. Then take a reading of your 4.01 Buffer and write that result down. Let me know what your meter reads.

I'm only using 4 and 7 buffers since this is for brewing.

As mentioned in the first post the meter is brand new, but i did purchase it about a year ago. It didn't come out of the box until this past weekend

You can teach a man to fish.... once i have my 4 and 7 buffer readings with the calibration erased, what do i need to calculate? What am i looking for? I'm good at math so no need to simplify if it's complex.

 

[Hanna_Brewing]

So...here's a question: is there a dry shelf-life for this type of pH probe?
Meaning, from its build date to date of first use, can a probe time-out before it's even sold?

Cheers!

On Average i'd say a pH electrode lasts 18-24 months but that's relative to how well it's preserved, cleaned and the type of application.

If you measuring hot acids you might not see it last as long as if your sample was more neutral in composition and temp. In the end though, as long as your slope and offset are in spec you have a good probe.

If its not calibrating, this could just be a dirty probe or clogged junction. I would try using a cleaning solution and slightly pulling on your cloth junction before ruling it out as a now "dead probe." And of course, after using cleaning solution, re-hydrate it.

 

[ajdelange]

...what do i need to calculate? What am i looking for? I'm good at math so no need to simplify if it's complex.

Not complex at all.

The response from a pH electrode is

E = Eo - 58.167*slope*(T + 273.15)/293.15) )(pH-pHi)

where Eo is small number (the offset - a few mV), slope is a number near 1 and pHi is the isoelectric pH of your electrode. Assume it is 7 as that's what your meter does. T is the temperature in °C. When your meter is calibrated it has values for Eo and slope and is thus able to solve the equation above for pH given E, the electrode response. If you 'clear the cal' in the meter you are, I presume, setting Eo to 0 and slope to 1. Measure the pH of the two buffers and calculate the corresponding E values for both.

E4 = 0 - 58.167*1*((T + 273.15)/293.15)*(pH4-pHi)
E7= 0 - 58.167*1*((T + 273.15)/293.15)*(pH7-pHi)

where pH4 and pH7 are the meter readings

Now using the two calculated voltages E7 and E4 solve the pair of equations

E4 = Eo - 58.167*slope*( (T + 273.15)/293.15)*(pH4b-pHi)

E7 = Eo - 58.167*slope*(( T + 273.15)/293.15)*(pH7b-pHi)

where pH4b and pH7b are the actual pH's of the 4 and 7 buffers at T as calculated by the formulas in the sticky, for Eo and slope. Voila!

 

[mabrungard]

For pH meter owners with a BNC-connected probe, there is a quick way to assess the offset that your probe is requiring. As mentioned above, the amount of offset is an indicator of probe health and quality.

Calibrate your meter and probe with 4 and 7 solutions. Then remove the probe at the BNC connector and short the meter's center and outer connections with a paper clip or other conductive metal. This is safe for the meter and the resulting meter reading provides you with an indirect reading of the offset. In essence, the meter should read between 6.5 and 7.5 if your probe has an offset of less than 30mV. If your shorted meter reading is outside that range, its time for replacement. When shorted, a perfect meter reading would be 7.00.

 

[ajdelange]

For pH meter owners with a BNC-connected probe, there is a quick way to assess the offset that your probe is requiring.

This is a little troubling, especially the way the statement is worded. A pH electrode does not require an offset. It produces an offset which must be taken into account. At the same time the instrumentation amplifier in the meter has an offset and that must be accounted for too. At first blush I would say that if you short the input terminals and read 10 mV then you are reading the offset of the instrumentation amplifier which has nothing to do with the offset of the electrode.

In the old days one accounted for op-amp input offset by supplying an equivalent voltage of the opposite sign which canceled the amp's self offset. the offset of the amplifier then appeared to be 0. In a modern piece of gear one could obviously measure the input offset and send a signal to a D/A converter to produce the cancelling voltage. Or subtract it out in software/firmware or just consider it to be part of the electrode's offset voltage and proceed as if it were actually 0. I have no idea as to which of these approaches if any is taken by any particular manufacturer.

You must have gotten this idea from somewhere which means you must know something I don't know but I am very interested. Please pass on more detail.


If your meter reads mV directly then it is an easy matter to solve the equation pair for slope and offset using the mV readings in the two buffers and the actual pH's of the buffers at the given temperatures. If your meter doesn't display mV then you can calculate them from the pH reading but to do so you must know what the offset and slope values are for the meter. Apparently 'cancelling' the cal on a Hanna meter sets these to respectively 0 and 1 so you can go ahead. I don't know how to 'cancel the cal' on any other meter. Many meters report Eo and slope and in those cases you can, of course, calculate them but why bother as the meter does that for you.

If you short the input terminals of the meter the reading is, AFAIK know at this point, going to represent the offset of the meter itself. If that is x mV (you can convert a pH 7 reading to an approximate offset voltage just by dividing the difference between 7 and the reading by 58.167) and the calibration process comes up with an offset of y mV you can conclude that the electrodes offset it y - x. Typical input offset voltages for the first instrumentation op amp spec sheet I came up with seem to range between -20 and +40 uV - small relative to electrode offsets that are mV or 10's of mV.

Interesting but puzzling!

 

[mbobhat]

No. Do it with the buffers. They don't change in pH over time. They do change with temperature but they change less with temperature than solutions of acid. Also buffers have high buffering capacity at their design pH's. Vinegar, for example, does not. This means that the buffer will resist pH change from external stress better than vinegar will. That's why we calibrate with buffers rather than with just acid.

I wasn't telling him to calibrate with anything but the buffers,
just was telling OP that if your buffers are drifting then a wort like sample such as vinegar may drift by a lot more than the buffers. Obviously you want something with some ions in it, not DI or very clean tap water, which will drift considerably.

Just a quick and dirty way of seeing if your meter needs TLC. When we measure pH for clean water act wastewater, we do two consecutive readings and they have to be within .1 of each other. Usually .05 is even better. Our probes are good probes though, double junction Orions, your results may vary. We are measuring RO wastewater, which where we live is not all that more concentrated than TAP, we adjust the temp between 24 and 26 degrees C, and usually get within .02 of each other two consecutive sample readings after two min equilibration.

 

[day_trippr]

On Average i'd say a pH electrode lasts 18-24 months but that's relative to how well it's preserved, cleaned and the type of application.

That scope covers my current probe - it's roughly 20 months old and has seen a lot of use. It never saw test sample temperatures above 80°F, was regularly cleaned after use in brewing with the Hanna cleaning solution, and stored with the Hanna storage solution. But it sounds like it may nearing the average lifespan.

But my question was regarding brand new replacement probes and how long they can sit on a retailer's shelf without significant degradation. Can you talk about that?

If its not calibrating, this could just be a dirty probe or clogged junction. I would try using a cleaning solution and slightly pulling on your cloth junction before ruling it out as a now "dead probe." And of course, after using cleaning solution, re-hydrate it.

Two evenings ago I soaked the probe in the Hanna cleaning solution for a half hour, rinsed it in distilled water, then set it in the Hanna storage solution for ~24 hours. Last night I tested it against a water sample and it took roughly 15 minutes to finally stabilize. No real improvement.

Should it sit in the cleaner longer or the storage solution longer?
Or is it pretty much toast?
I'm guessing toast...

Cheers!

 

[ajdelange]

I wasn't telling him to calibrate with anything but the buffers,
just was telling OP that if your buffers are drifting then a wort like sample such as vinegar may drift by a lot more than the buffers.

I got that. I thought you were suggesting that he check stabiity with vinegar and I was just pointing out that one of the buffers would be more stable. Now what you could do with vinegar is drizzle a little NaOH solution into it until the pH reaches something in the vicinity of 4.76. You have now made an acetate buffer which will be quite stable whatever its pH. And it is closer to mash pH than the 4 buffer and so you might argue makes a better buffer to check stability with.

 

[ajdelange]

Should it sit in the cleaner longer or the storage solution longer?
Or is it pretty much toast?
I'm guessing toast...

Cheers!

You are probably right but were it mine I'd let it soak in the storage solution for a few more days and give it one more shot. Perhaps the problem is that the reference electrolyte was drawn though the rag junction and the liquid evaporated. I'm hoping that if placed in the proper solution long enough there might be some migration in the reverse direction. I don't hold out much hope for this approach but what have you got to lose?

 

[day_trippr]

You are probably right but were it mine I'd let it soak in the storage solution for a few more days and give it one more shot. Perhaps the problem is that the reference electrolyte was drawn though the rag junction and the liquid evaporated. I'm hoping that if placed in the proper solution long enough there might be some migration in the reverse direction. I don't hold out much hope for this approach but what have you got to lose?

Worth a shot, and thanks for this and the earlier advise. I'll dunk it immediately and let it go a few days and see what happens.

Is there anything that can be observed - even under a microscope (I have one) - that might provide a clue?
[edit]Like, an air bubble inside the glass?



I'm guessing that isn't great...

Anyway, given the sensor may be at a reasonable EOL my greater concern is buying a replacement that's DOA.
Maybe best to buy directly from Hanna in the hope of obtaining a reasonably fresh probe...

Cheers!

 

[Hanna_Brewing]

That scope covers my current probe - it's roughly 20 months old and has seen a lot of use. It never saw test sample temperatures above 80°F, was regularly cleaned after use in brewing with the Hanna cleaning solution, and stored with the Hanna storage solution. But it sounds like it may nearing the average lifespan.

But my question was regarding brand new replacement probes and how long they can sit on a retailer's shelf without significant degradation. Can you talk about that?

I can't really say with certainty and the reason is this: We've always believed that timeline to be up to 2 years. Mettler Toledo states on their website that it will last up to one year. And of course, this is assuming the probe is kept with storage solution in ambient temperatures. If it's let to freeze, over heat or dry-up too long that could change the timeline. But overall, slope and offset are your best determining factors regardless of time. If slope is between 85 - 110% and Off Set is +/- 30 mV then you have a good probe.

Two evenings ago I soaked the probe in the Hanna cleaning solution for a half hour, rinsed it in distilled water, then set it in the Hanna storage solution for ~24 hours. Last night I tested it against a water sample and it took roughly 15 minutes to finally stabilize. No real improvement.

Should it sit in the cleaner longer or the storage solution longer?
Or is it pretty much toast?
I'm guessing toast...

Cheers!

I wouldn't say to soak it for any longer in cleaning solution. Actually most of our cleaning solutions say to soak from 15-30 minutes; it depends on the type of solution. The proteins cleaning solution is best for beer applications but I would also recommend you pull that cloth junction just a bit so that the reference is cleared out. If it’s clogged that can be a problem. Overnight hydration is perfect and should do the trick but soaking longer can only help so if you think it needs to hydrate more certainly try it out. If after all that it won’t calibrate than you're probably right...it may be toast. Try to keep your probe up right if you can. I'd suggest letting it sit in a beaker and make sure the probe is fully submerged when cleaning, storing or calibrating. Staying up right makes sure the internal solution is dropping to the bottom so that it fully interacts with the bulb and your sample. You could even try shacking it down like you would a thermometer to make sure no air bubbles are caught at the bottom.

 

[ajdelange]

Then remove the probe at the BNC connector and short the meter's center and outer connections with a paper clip or other conductive metal.

Never mind the request for further information. It came to me this morning (i.e. a day later as is often the case).

The meter displays, after determining Eo and slope:

pH = pHi + (E - Eo)/( 58.167*slope*((T + 273.15)/293.15) )

When the input is shorted E = 0 and so the meter displays

pH = pHi - Eo/( 58.167*slope*((T + 273.15)/293.15) ) =

7 - Eo/( 58.167*slope*((T + 273.15)/293.15) )

as all meters assume pHi = 7.

Thus you can approximate what value your meter is using for Eo from

Eo = (7 - pHdisplayed)*( 58.167*slope*((T + 273.15)/293.15) )

The reason it's an estimate is that you don't know the slope the meter is using. So just use

Eo = (7 - pHdisplayed)*58.167

The other uncertainty is due to the fact that Eo is the sum of the instumentation amplifier's offset and the electode's. With current op-amp technology the effects of bias currents are largely eliminated and you should see mostly the electrode.

The second part of Martins approach is to apply E = 58.167*((T + 273.15)/293.15) ) mV (there are pieces of test equipment made for testing pH meters that supply small voltages like this) to the meter when the temperature probe reads T. The meter reads

pH = pHi + (E - Eo)/( 58.167*slope*((T + 273.15)/293.15) )

you know Eo and can thus calculate slope.

 

[schematix]

Not sure what's going on here but I suspect i have a useless $100 pH meter now.

I erased the calibration and received the following data points after 10+ minutes of soaking in the buffer:

4 Buffer: @18.2C measured 3.97 (4.00 expected)
7 Buffer: @18.6C measured 7.00 (7.02 expected)

Great! So looks like only a very slight offset exists.

I think it might be time to pour an IPA and re-test the auto-cal.

Before i even poured the IPA I went ahead and did an auto-cal routine. The meter had been soaking in the 7 buffer for about 20 minutes when i started. It accepted the calibration for the 7 buffer within a few seconds. So i rinsed with tap water, DI water, shaken and dried, and put into the 4 buffer. Another few seconds later it accepted the reading. And then the reading plummeted down to 3.92 over the course of a few minutes:

View attachment ImageUploadedByHome Brew1486704720.950911.jpg

wtf.

So i deleted the calibration, and now it reads 4.08...
View attachment ImageUploadedByHome Brew1486704747.268348.jpg

wtf. ok maybe the buffer was contaminated. so then i poured a brand new sample of buffer and the meter is now reading 4.12!

View attachment ImageUploadedByHome Brew1486704762.568209.jpg

wtf.

all of these pictures above are after at least 5 minutes of sitting. between measurements samples were rinsed with tap water, DI water, shaken and dried (bulb not touched).

 

[Hanna_Brewing]

Not sure what's going on here but I suspect i have a useless $100 pH meter now.

Hi Schematix, I can't be certain because of the angle of the pictures but it looks like to me that you need to add more buffer into your beaker for calibration and testing. The probe needs to be completely submerged in order to get a proper reading. Try that to see if it improves your readings.

 

[schematix]

Hi Schematix, I can't be certain because of the angle of the pictures but it looks like to me that you need to add more buffer into your beaker for calibration and testing. The probe needs to be completely submerged in order to get a proper reading. Try that to see if it improves your readings.

The angle plus the refraction of the beaker gives a false impression. They were fully submerged.

What else can i try?

 

[ajdelange]

Not sure what's going on here but I suspect i have a useless $100 pH meter now.

I erased the calibration and received the following data points after 10+ minutes of soaking in the buffer:

4 Buffer: @18.2C measured 3.97 (4.00 expected)
7 Buffer: @18.6C measured 7.00 (7.02 expected)

Great! So looks like only a very slight offset exists.

I got all excited when my cell phone only displayed up to this point and proving that confirmation bias is as strong here as anywhere else I read "useless" as "usefull". Yes, that looks great. Small offset and slope close to 1.

Before i even poured the IPA I went ahead and did an auto-cal routine. The meter had been soaking in the 7 buffer for about 20 minutes when i started. It accepted the calibration for the 7 buffer within a few seconds. So i rinsed with tap water, DI water, shaken and dried, and put into the 4 buffer. Another few seconds later it accepted the reading. And then the reading plummeted down to 3.92 over the course of a few minutes:

And then I saw the rest.

This change is due to the unfortunate design flaw in the way this meter does calibration. This behavior is common for this meter and stems from the fact that, especially as an electrode ages, its response slows. Even with a brand new electrode of unusually good response characteristics calibration readings should not be accepted for at least 30 seconds and, for precise work, for a couple of minutes. The pHeP meter electrodes are actually pretty stable and so suitable for brewing if this calibration problem were fixed. It is only because of that flaw that this meter is not in the group of 'HBT vetted' meters.

This problem is exacerbated if the electrode is, because of age, mishandling, poor storage, improper hydration, unusual flood stages in the Nile.... unstable so I'd say best check that next. Disable the cal and immerse in 4 buffer. Record the indicated pH every couple of minutes at first, then every 5, then 10 and so on. The variations you see will guide you. You will be looking for trends and random fluctuations. A trend is, if not too steep, acceptable. "Noise" about the trend line of more that ±0.02 or so is not. Too much noise or too much slope (more than 0.02/hr after 5 minutes) means that the electrode is not stable enough for use.

BTW if you use a stir plate this will introduce what is imaginatively called 'stirring error'. If you use one when calibrating your calibration will take out the stirring error and readings on samples will be off by the stirring error unless the sample is subject to the same stirring error. So it's OK to use a stir plate as long as the sample is subjected to the same stirring as the buffers were during cal. Better practice is to move the electrode about in the solutions (buffers or samples) to make sure that rinse water in the vicinity of bulb and junction is displaced by buffer or sample and to repeat this process every few seconds in order to establish equilibrium of the reference fill with the sample.
During stabiity check measurements repeat this process about a minute before you record the pH measurement.

Temperature is important. Put the buffer in a water bath of some sort if you can but record temperature at which each reading is take. An example of a stability test data set is at https://www.homebrewtalk.com/showthread.php?t=302256