It's a Hanna HI 99104 pH meter. It has 2 dials for calibration. One for 7 and one for 4/10.
I have new calibration liquid. I dip pen in pH 7 and adjust the "7 trimmer" to 7.01 (the exact pH of that liquid at that temp).
but when I put the pen in the pH 4 solution, I cannot bring the pH lower than 5.5 by adjusting the 2nd (4/10 pH) trimmer.
If I adjust both the 7 and 4 trimmer, I can fix up the pH, but then if I put the pH pen back into the pH 7 solution, the pH is off on that and won't be able to go back down to 7 unless I adjust the 4/10 trimmer as well.
Basically - it won't calibrate! It's not too old but has only been used about twice, got it brand new before that. The electrode dried up during storage (months) though.
I have new calibration liquid. I dip pen in pH 7 and adjust the "7 trimmer" to 7.01 (the exact pH of that liquid at that temp).
but when I put the pen in the pH 4 solution, I cannot bring the pH lower than 5.5 by adjusting the 2nd (4/10 pH) trimmer.
If I adjust both the 7 and 4 trimmer, I can fix up the pH, but then if I put the pH pen back into the pH 7 solution, the pH is off on that and won't be able to go back down to 7 unless I adjust the 4/10 trimmer as well.
Basically - it won't calibrate! It's not too old but has only been used about twice, got it brand new before that. The electrode dried up during storage (months) though.