My buddy keeps finding stuff from his dwindling stash (my fault that it's dwindling). The latest is an early 70s Erisman PACEMETER, "The Human Performance Monitor". What a gadget! Two analog meters in a case, the left for MPH and the right for RPM. Uses 3 sensors on front spokes with a pickup on the fork for MPH; for cadence (RPM) it uses 5 magnets that bolt into the inner side of the chainwheel with the pickup clamping onto the seat tube. "Over two years of research and testing have gone into the development of this product.....we are cycling enthusiasts and are anxious to help you get maximum service from your PACEMETER." Erisman Industries, Inc., Warrensburg, Missouri.
Only a few references in archives so thought I'd add to what is there.
Angel Garcia
Long Valley, NJ