Instructions and a visual diagram for hooking up 3 #5540 batteries to power a Beckman Model G pH Meter. These three smaller batteries could replace a single, large 22.5 volt battery. This diagram was written on Bob Fairburn's stationary, but there is no other evidence that it was drawn by him.

Arnold Beckman invented his first pH meter in 1934 at the request of a chemist from the California citrus industry, who needed an accurate way to measure the acidity of his product. The resulting “acidimeter” with its glass electrode was renamed the Model G pH meter in 1937 and produced on a larger scale by Beckman’s company, National Technical Laboratories. This instrument kicked off the rapid development not only of NTL and Beckman Instruments, but also of the electronic scientific instrument industry.