[Radio Wrangler]

They were used for measuring voltage of course. Anywhere for any purpose, but the range marked gives some idea of where it would be useful.

The scale would fit the sort of voltages seen on a 24v battery bank. There would be no interest below 10v that would mean dead flat. The nominal voltage on charge would be around 28V, so the scale has some range for fault conditions.

The even spaced markings would fit with a d'Arsonval moving coil mechanism, which would read DC.

AC was measured with DC instruments using little copper oxide rectifiers, and the meters would not read well until the rectifiers were being driven adequately, so a blank bit of scale at the bottom was not unusual. So that opens up other possibilities. Judging the spacing from zero to 10v, which is disproportionate to the rest of the scale, maybe it was used for AC with a rectifier

It's in the nice quality rather than extra rugged category, so it was probably for a fixed use.

Lots and lots of possibilities, so few clues.

Worth? not a great deal, unless it had some specific and important history.

David