In article ,
David Nebenzahl wrote:
I have an old galvanometer (nice Weston in a slant-front black crackle
case). Its scale reads 30-0-30. What units are these? Or are they just
relative values for comparison?

Most meter *movements* will only read directly small currents or voltages.
To allow them to read higher values you use an appropriate resistor - in
series to read a higher voltage than the FSD of the movement or in
parallel to read a higher current.

So the exact same movement can be supplied with a variety of scales for
different applications - and may or may not include this resistor, which
is called a shunt for current and multiplier for voltage. If it includes
this resistor the scale is usually marked with the true units.

30-0-30 was common for the ammeter on older cars.

--
*The average person falls asleep in seven minutes *

Dave Plowman London SW
To e-mail, change noise into sound.