You can easily determine if the meter is a remote reading meter or one with
a built in thermocouple. Put a digital ohmmeter on the meter leads. if the
resistance is very low, then the thermocuple is built in. If the resistance
reads tens of ohms or more, it is a simple dc meter that can be used for any
purpose.

I have found that many of the remote reading meters are not calibrated in
actual amps, but are relative reading.

Often the rf ammeters that are self contained contain a bakelite or formica
back to give clearance to the rf.

Colin K7FM