Directions for calibrating a McLeod gauge for use with the early model of the Beckman pH meter. This letter is likely related to the handwritten McLeod gauge diagrams and calculations also found in this folder. At the time of this letter, Joseph was a researcher for the California Fruit Growers Exchange.

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 instrument kicked off rapid development not only of Beckman Instruments, Inc. but also of the electronic scientific instrument industry.