Read more about it here:
Is that the same Onan that makes gensets?
Same Onan that makes generators, although now it is called Cummins Onan.
Onan Wrist Meter patent . . .
David W. Onan
Apparatus for Testing Electrical Systems
Patent number: 1513672
Filing date: Nov 13, 1920
Issue date: Oct 28, 1924
Would love to see one and hear how it worked if anyone has any "first hand" experience with one.
I wonder what time span these were produced and in what volume? There must be a few survivors.