ok you have a point there.
Tomorrow I will get some fluid with PH 9 or 10.
But it is still strange that I cannot calibrate a new probe,
to ph4 !!

I tried with an old probe, and I cannot get this one lower than 4.5,
I then put some lemonjuice in water, tried the old probe and... 3.5.
I guess there is something wrong with the calibration fluid provided with
the probe!
I'll try again tomorrow.


"Pszemol" wrote in message
...
"Arjan Bakker" wrote in message
...
I don't think it matters,
in my opinion you calibrate the slope mv/ph.
If the ph value is below 7 the mv/ph is negative,
above 7 is positive. But the slope stays the same.
At least this is what I remember from chemistry-lessons.
(a long long time ago!!!)

In an ideal world - maybe... :-)

But real probe does not have linear characteristic
so it is a curve. If you want acurate measurements
you are interested in calibrating the meter as close
to the measured value as possible...