Harmonic Wave Analyzer 300A, 1941
The 300A measured the individual harmonic present in the output voltage of an amplifier. It consisted of a balanced detector, a local oscillator and a tuned amplifier. Galvin Manufacturing Company, maker of Motorola radio equipment, was an early customer.
Note the wooden case. In the early 1940s it was customary to have measurement equipment in wooden cabinets. Most cabinets were made of walnut, but Bill Hewlett and Dave Packard decided to use oak. As HP enlarged its line, Bill and Dave gave up using wood because it served no useful purpose and added to the cost.