This is the
Radio Shack® 22-216 autoranging multimeter. This is a very strange multimeter. Autoranging is not a feature commonly found on analog deflecting meters. As this meter is powered, it also uses op amps to amplify the signal. With the op amps, the actual impedance of the meter is not visible to the user - the user sees a FETVM or VTVM impedance of 10MΩ. This is the case for all voltage ranges except for the manually selected 300mV ranges where the impedance goes down to 1MΩ.
As this has digital ICs and op amps, this has several features that make this better than regular multimeters and VTVMs. One is that it uses op amps and implement a precision rectifier - and thus the low voltage AC scale matches that of DC (though not true RMS). It also supports automatic negative voltage measurements - if the probes are reversed, the negative LED lights and the meter measures as if the probes were reversed. And of course the autoranging - if the meter detects that the voltage is over range and it's not locked, it will upscale or downscale to make sure the meter does not show '0' or peg off scale. The upscale/downscale buttons can be used to force it to change the range if another range can also show the reading without pegging the meter. The yellow disable autorange button can force it to not change ranges. As the meter changes ranges, 5 LEDs on the meter face will show what range the logic selected.
The meter will autorange DCV, ACV, and ohms. The 300mV AC/DC range is selected by the knob and does not autorange. The 300mA/3A AC/DC current modes also will not autorange (select by changing probe plug locations). Note that the 3A AC/DC modes is unfused, so expect damage if you exceed the range. The meter also has a continuity buzzer and an internal battery tester range.
As this is an autoranging meter, it has digital electronics and requires power. It requires four UM3 (AA) cells to operate the meter in any mode. The battery power rating is 15mA max; I measured around 6mA when idle, no doubtedly the LED and leakage of the op amps were the worst offenders. This translates to around 150 to 350 hours of battery life - which is fairly horrible compared to modern LCD digital multimeters.
Ranges
(5+5) 3V, 12V, 60V, 300V, 1000V autorange AC and DC (10MΩ impedance)
(5) x1, x10, x100, x1k, x10K ohms (about 1.2V bias, and 5.7mA in the x1 scale)
(1) Beep Continuity (no autorange, of course)
(2) 300mV AC or DC (1MΩ impedance)
(2+2) 300mA or 3A, AC or DC
(1) Internal Battery Test
"23 Ranges" (one is the internal battery test... what a range! Really should be "22 ranges")
The meter has a mirrored scale and is about 1.5" thick. A swivel handle/stand along the top. This is a lot thinner than the Heath V7A VTVM and Eico 555 multimeters, as it uses a PCB with surface mount devices unlike the older multilayer wafer switch design. This unfortunately means that it can't really be set upright, though the handle can be folded so the meter rests at an angle. The slide power switch is on the left that turns the power on to the ICs and LEDs. At least one LED on the meter face will always be lit when the switch is on, indicating the meter is always eating the batteries when on. There appears to not be a auto-off so expect having to replace batteries often if you forget to shut it off.