this thread is interesting, I was going to start a new thread with some q's about my Milwaukee pH meter but I'll hijack 'em into this one....
I have the MW102 http://www.amazon.com/Milwaukee-MW102-14-00-%C2%B5P-Based-Meter/dp/B001DTNDME/ref=sr_1_1?ie=UTF8&qid=1330785089&sr=8-1
which is just the MW101 that others have, with ATC (I believe this is an update of the SM101 and SM102 line which major has?)
anyways this is what happens which i check mash pH... I'm just copying in notes from an Altbier batch about 2 wks ago: "calibrated meter to 7.01 and then 4.01 buffers. read pH of 5.46 @ 24.7*C. then put meter in 4.01 buffer. it reads 3.79. now checked 7.01 buffer, it reads 7.03. now back into mash sample, it reads 5.63 at 21.6*C." (my brew room is about 55F this time of year so the sample keeps cooling as I'm checking it)
and from 1 month ago, a Boh Pils: "calibrated meter to 7.01 and then 4.01 buffers. read pH of 5.27 @ 28.9*C. then put meter in 4.01 buffer. it reads 3.73. now checked 7.01 buffer, it reads 6.89. now back into mash sample, it reads 5.34 at 20.7*C."
now maybe this is all within the margin of error for this meter and probe, and it's all "good enough" and I should RDWHAHB etc etc... although I am one who likes to know that what I am getting is really what's there... or what are you other guys with Milwaukee meters seeing? I use the Hanna storage solution, and the Hanna 4.01 and 7.01 buffer packs from Amazon (I once called Milwaukee and they said it is OK to use Hanna products on their meters)
finally, if mash pH does change during the mash, when do you check it??? I asked this a bout a year ago on this forum, and it seems like most people take it about 5 or 10 minutes after dough-in? of course it takes 10-15 minutes for the sample to cool (I try to consistently read pH around 20-25*C [68-77*F] even though I have ATC). what are you guys doing about this?