2009/6/29 Thomas Giannou <thomas@...>
>
> After the meter is
> calibrated, those two calibration fluids should read 7.0 or 4.01 with the
> meter in read mode. If the readings of the meter are outside the
> percentage of accuracy when measuring the 7.0 or 4.01 calibration fluids...

I am going to butt in and add emphasis to what Thomas is saying. The
calibration process with the commercially bought reagents is one part.
When complete, the operator then is supposed to check the calibration
process itself by switching the meter OUT of calibration mode. Then
drops of the calibration reagent are reapplied as if they were samples
to be tested. If the "reading" is outside the accuracy limits of the
meter the whole meter or the probe must be replaced.

Thomas and Jody are speaking of high-quality two-drop meters Bob Pike
came across that became an instant hit with the RBTI agricultural
people. Plant sap analysis can tell the ag consultant so very much,
but it is so very hard to get a few drops of plant juices and the
samples are almost always tainted with color. The two-drop pH meters
overcame both hurdles and were, naturally enough, used for
urine/saliva testing by those who did both services. However, this
"good thing" was not so good in the hands of urine/saliva only people
because they tend not to be fanatical enough about the need to
calibrate...calibrate...calibrate.

It should be added that the archives will reveal that most of this
discussion is a re-hash from years ago. I believe the final thought
then was that the reagents are the "gold standard," but that should
not hinder the users of quality meters as long as they calibrate
properly---and often.

Some people use pH paper and do well enough. I personally find the pH
Stix worthwhile and have found that kids handle them like a pro while
making few errors. It is a good thing when an 8 y.o. can get a decent
result after about 15 seconds of instruction. I like to think that
Reams might have given pH Stix a big nod after realizing after a long
day's class with reagents that some people still didn't get accurate
results.

Regards,
Rex Harrill