OK, now I'll respond to the current post:
I've been doing AG for a bit now and am interested in tinkering with water additions and pH. I'm wondering if anyone has now tried the
$70 Hach Pocket Pro pH meter (model no. 9531000)? I understand that it has a significantly lower accuracy (± 0.1 pH vs. ± 0.02 pH) than the
$115 Pocket Pro + (model no. 9532000), but wonder how important that difference is in the context of mash pH measurements (i.e. if I get a reading of 5.2 with the cheaper meter, does it matter that the actual pH could be as low as 5.1 or as high as 5.3?)
In the case of the Pro + we know exactly what the accuracy specification means as Hach sets it out clearly in the 'manual'. BTW this is the only time I have ever seen the meaning of a pH meter manufacturer's definition of accuracy stated. It means that a freshly calibrated electrode returned to one of the buffers with which it was calibrated will give, over a specified period of time, readings whose RMS error is the stated value. Thus if they quote 0.01 (and as I remember that's the value given for the +) the standard deviation in a reading's error (if made withing the spec time frame) will be 0.01 pH. The plot in the post at
https://www.homebrewtalk.com/showthread.php?t=302256 shows what this means. There we see errors of up to 0.03 though most are less than that. The square root of the sum of the squares (RMS) is, however, less than 0.01 and so the 0.01 accuracy spec is met.
(i.e. if I get a reading of 5.2 with the cheaper meter, does it matter that the actual pH could be as low as 5.1 or as high as 5.3?)
Or more. Imagine the errors in the plot in the Sticky to be 10 times what the scale indicates. Thus would imply accuracy of 0.1 pH rather than 0.01 using the numbers as plotted.
The interpretation of all this is that, as modern digital electronics don't drift, that accuracy is really completely (or mostly) determined by the stability of the electrode.
Electronics manufacturers don't like to build 10 different instruments for a line of products. It is often much less expensive to build one an 'cripple' some of the functions it is inherently capable of. Hach may (and I emphasize may) be doing something like this by which I mean the whole line may be one circuit. If one orders the pH only version the conductivity circuit may be disabled and a pH electrode slapped on the thing and it ships as a Pocket Pro + if it meets the 0.01 spec. If it doesn't, then move a jumper (which disables the hundredths digit and renders it a Pro rather than a Pro +) and send it to shipping. Just speculating here but I do feel quite assured that if you go with the cheaper unit you will have an unstable (to the extent of 0.1 pH standard deviation) meter and you will realize that 'the bitterness of poor quality remains after the sweetness of low price is forgotten).
In other words, I'm wondering if the extra accuracy is really worth an extra $45,
Yes, it absolutely is. Though you don't need 0.01 or 0.02 absolute accuracy in brewing you do want to be able to see the effects of water or mash treatments to that level and, therefore, need the higher resolution/accuracy/stability.
..given that I'll be using the pH meter exclusive for homebrewing and won't have other occasion to take advantage of increased accuracy.
You might be surprised.