What Is This? Exploring a Mystery Hewlett-Packard Instrument From 1950

I was about to call this an “early Hewlett-Packard product”, but that wouldn't be correct. Hewlett-Packard was founded in 1939 and by 1943 already employed 200 people manufacturing a line of electronic test equipment sold to industry and the military. This indisputably is, however, an odd Hewlett-Packard product.