Many panel meters will have, in small print at the bottom of the faceplate, something like "FS=1ma". This would indicate that the base meter movement is 1 ma full scale. beyond that, there could be series resistors internally for a voltmeter. For ammeters, some have internal shunts, generally for 1 amp or under. Others will require an external shunt.
As stated, use a series resistor to get a reading. Once a resistor value in combination with a know voltage you can determine the movement's scaling. Typical meters, w/o internal resistors or shunts, are 1ma or 100 ua FS.
My uncle worked for Weston as a first job until he retired. As a result I acquired quite a few analog meters of various sizes, scales and shapes. His work highlights were assembling and testing panel meters for the Gemini and Apollo capsules. He received a commemorative medal for his work made from aluminum that was taken from some part of the spacecraft that orbited the moon. The aluminum was melted with a quantity of virgin metal and used to produce the medals.
Paul