Now here is an interesting device, Frigidaire made the similar tests units from the Multimatic up...
http://www.ebay.com/itm/Vintage-196...515?pt=LH_DefaultDomain_0&hash=item27ca5d389b
http://www.ebay.com/itm/Vintage-196...515?pt=LH_DefaultDomain_0&hash=item27ca5d389b
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