What is this?

[got10carz]

Volt meter says Readrite Meter Works Bluffton Ohio.
With the 22 1/2 highlighted makes me wonder if it's for checking Mag output?

[TWrenn]

Bluffton Ohio!...thats Forum member Jack Putnam's neck of the woods!

[Jerry VanOoteghem]

It's for checking radio batteries. In the early to mid 20's, radios were battery powered. They used "A" batteries for the tube filaments @ 6V, and "B" batteries for the tube "plate" voltage, with taps for 22-1/2 & 45 volts.

[Erik Johnson]

It's a typical 1920s pocket DC voltmeter.

It won't work for checking Model T mag output which is AC.

It can be used for a variety of applications, not just radio batteries.

It's a common item - not rare. I have a couple of them and regularly see them at estate sales and swap meets. I also have a pocket ammeter.

They usually have a wire with a probe attached to the top terminal or a permanently attached wire.

[mtntee20]

NOTE: While it would work for 6 volt batteries, it would not be too accurate. ALL gauges and meters are most accurate at approximately middle of the face range. Thus, the 22.5 volt spot, would be accurate while the 6 volt and 45 volt reading would be "close" but not as accurate as 25 volt, exactly at mid range.

Thus, the designer had determined the 22.5 volt reading as being the most important, to ensure proper operation of the device being inspected, but required a 50 volt maximum to include the 45 volt secondary inspection point. Starting the range at 0, the meter could be used for low voltage DC measurements and MIGHT be close enough OR just serve as a "Go / No Go" indicator.

[Jerry VanOoteghem]

I don't think anyone expected or needed this to be a precision instrument.

[John Codman]

For years I had a Zenith Wavemagnet radio that looked like a small suitcase and it had two batteries - one of which was a 90 volt "B" battery. If you touched both terminals once, you would never do it again. I wish that I knew what happened to it.

[TRDxB2]

Looks like this when complete with all its parts
https://www.ebay.com/itm/166920629637?_ ... 1506.m1851

[mtntee20]

I don't think anyone expected or needed this to be a precision instrument.

My guess is that 22.5 volts isn't accurate enough.

[Jerry VanOoteghem]

I don't think anyone expected or needed this to be a precision instrument.

My guess is that 22.5 volts isn't accurate enough.

Not sure what you're getting at. If you've ever operated an early 20's radio, you would notice that they'll operate just fine at anything even close to the specified voltages. For that purpose, this volt meter is more than adequate.