John Kiernan's comments were right on.

For those of you who do pH papers, there is this possibility.

What do you do about the person who is color blind and cannot 'see' the color
to indicate correct pH?  Plus do papers have expiration dates.  I gave up them
years ago when it became apparent there were subtle discprencies in reading the
colors, plus what about dyes (obscuring those colors, talk about a proverbial 
monkey wrench tossed into the pot) in the solutions you are test?  You could
call this "blind trust"???

pH meters aren't that expensive and so easy to calibrate.  

A pH meter should be standard equipment in a laboratory, the same as a
microtome, processor or technician (yup, I often feel like a piece of
equipment!)

Gayle Callis