AVO electric avo meter EA 113
Another unusual model, the Electronic Avometer (EA113) incorporates an amplifier to increase the sensitivity of the instrument. It could be used on high impedance circuits without affecting either the operation of the circuit or the reading of the meter. The ordinary AVOs could not do this, but we tend to forget these details nowadays when all multimeters have sensitive amplifiers. It has an unusual ohms range, too, which works in the opposite direction to normal analog meters, with zero ohms on the left and infinity on the right. The ohms adjustment control must be set (with the probes apart) to infinity, instead of the usual adjustment to zero with the probes shorted. In addition to that, the red terminal is positive when measuring ohms, whereas on a normal analog meter it would be negative on ohms ranges. In most DC ranges, the meter can be set to centre-zero instead of having zero on the left. In this mode, the knob on the right is used to adjust the pointer to an accurate zero in the middle of the scale. The scale is marked 1-100 in black and 50-0-50 in red, for use in centre-zero mode. This meter also has a wonderfully colourful case, in blue instead of AVO's usual black. Takes four AA batteries.