When did you last use a Tach Dwell meter?
Googling Fox Valley brings up the Fox Valley Metrology company- started in 1996, which seemed to be too late for this sort of meter. More googling brought up a earlier company- Fox Valley Instrument of Cheboygan Mi. which is now out of business.
Apparently no connection between the two companies, but with the similarity in names, one does have to wonder...