Inside a simple battery tester (with schematic)

A nice simple device for a change. This is a battery or cell tester that I've been using for a while.
It's extremely ungenerous in its test, so I've always used it as a rough guide as opposed to being an accurate indication of cell state.

Since Grant sent me a new one, I thought I'd take the old one apart, and decided to make a video about it.

I didn't remove the PCB from the meter in the new unit, but I did go back and measure the combined circuit resistance. So if you're up for a puzzle....

3 resistors in parallel measure 162 ohm. If the known resistors are 3820 ohm and 564 ohm, then what is the value of the unknown resistor. (The meter's coil impedance.)
Answer is at bottom of description. I think this may be a 2mA FSD coil.

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Mystery resistance is around 242 ohms.