Sorry AJ, you haven’t convinced me that I need ATC, or even that I want it.
No need to apologize. No loss to me. I'm not trying to convince you in particular that you should or should not have ATC. But I do need to make sure other readers are aware of the value of it. Were there none the manufacturers would not offer it because people wouldn't pay the 'premium' for it. It's not quite the same as Apple convincing people they need the new iPhone. pH meters are used by engineers and scientists capable of making informed decisions (for the most part). It is perhaps true that in a meter that uses analogue circuitry (potentiometers) for calibration gain and offset that ATC isn't justified because of the inherent inaccuracies/instabilities introduced by the use of analogue techniques but I don't suggest that people buy analogue meters either. There is a reason they have long been supplanted by digital.
If you don't appreciate the value of ATC I suggest that you refrain from buying meters equipped with it.
You might consider it a worthwhile feature, but it’s far from being a necessity.
I definitely do but then I've done error propagation analysis on pH measurement.
It’s more like $25. I like simple, mine has a power switch and two adjustment pots.
You do need the power switch but you don't really need the adjustment pots. Just a high impedance voltmeter will do. In fact that's how I use my lab pH meter. All it does is send millivolt and temperature readings to the computer. Of course the computer does ATC on the calibration and readings. I really can't imagine what sort of code I could write that didn't incorporate ATC. It's an intrinsic part of pH measurement.
How did easier turn into need it ?
Well a lot of people measure pH for a lot of reasons and as most modern meters are equipped with ATC I guess a lot of meter buyers think they need it. As noted above, if they didn't then the meter manufacturers would not be able to use it as a sales promoting feature. But then again as also implied modern meters use digital circuitry after a fixed gain instrumentation amp. The numbers from the A/D get inserted into microprocessor algorithms identical to the ones in my lab computer. ATC is an inherent part of this.
Beyond that I have lots and lots of thing I don't need in my brewery. It is those things by and large that make the difference between a day of drudgery and an enjoyable brewing experience.
I measure all my samples at room temperature, that’s just good practice. At room temperature ATC does nothing.
That's not so. Temperature compensation is being done whether you are aware of it or not. The meter has to know the temperature difference between the buffers (if any) and the temperature difference between the buffers and samples. The only case where no temperature compensation is required is where both buffers and sample are at exactly the same temperature. If I calibrate without ATC using an analog meter then I need to insure that the buffers are at the same temperature. That should be easy enough to do as I can just put them in a water bath. But then I (or the meter) must know the temperature of any sample I measure because the slope is directly proportional to temperature. If I'm using an old analogue meter I have to measure that temperature and dial it in with another potentiometer or bring the sample to very close to the buffer temps. If I'm using a modern meter it's done automatically (including the temperature measurement and I can focus on brewing - not correcting pH readings. I don't have to worry that one buffer was a little warmer than the other nor do I have to get the sample temperature exactly or very close to the buffer temp. Without temp. compensation 5 °C means 0.017 pH error. With ATC 10°C or more is close enough (subject to isoelectric pH being close to 7 and because of possible pHi variation one doesn't want to be too far from the buffer temperature - not to mention physical stress on the electrode). I like to take lots of pH measurements and, with ATC, I can do that with ease and have confidence in the numbers that go in my log.
In an analogue meter you control the gain and offset of operational amplifiers to set slope and offset and trim the gain by (Tsamp/Tbuff) to compensate for temperature. In a digital meter you solve a pair of linear equations (which may contain different buffer temperatures) and then simply multiply the slope by the ratio of buffer to sample temperature. Since you have to implement the equations anyway that is why all digital meters have ATC capability - it's automatically built in. I suppose you could figure out some way to 'cripple' the ATC so you can charge $25 to un-cripple it but as I've seen ATC equipped meters for under $80 I doubt anyone is doing that.
Looking at what I've just written perhaps the best reason to insist on ATC, then, is to be sure you have a meter than does calibration and interpretation of electrode signals digitally.
