Quote Originally Posted by Photo Engineer View Post
Mark, there is a test for this using small quantities of film. It uses standard clips of 35mm film. PE
Michael wanted to determine the minimum quantity of developer required for a roll (80 square inches). Can this be determined without developing an entire roll? I guess one could develop a 20th of a roll, for example, using a 20th of the developer, by holding the strip to the bottom of the tank using magnets. But a 20th of 100 ml is only 5 ml, and I wonder if I could reliably get such a small quantity to cover the bottom of the tank. Did you have something else in mind?

Anyway, the home-made pH-tester I built a couple of weeks ago gave me time to decide what I really wanted. Here's what I got for the reasonable price of US$53 on ebay:


It's odd: That electrode cost three times as much as the meter. I don't have a temperature probe for it, so I can't use ATC -- auto temperature compensation. So my calibrations and measurements are all done at 20C.

Also, I built a (hopefully) better baffle for holding fluid steady while developing test-strips. A strip is held to the bottom of the tank with magnets, and this baffle stops unwanted fluid-movement:


The short legs you see on the bottom are just tall enough to clear the magnets.