Vintage Heathkit Voltmeter.  This voltmeter powers on and the tube lights up.  No further testing was done with the unit.  It is in good cosmetic condition, with normal signs of age and use.  There is an old Eveready C battery inside would probably needs replaced.  Take a look at the pictures for more details and message me with any questions you may have.  EDIT: added a picture of the plug for all the plug experts out there.  Experts can determine plug originality and determine if this unit will suit your needs or not.