The principle of the meter is very simple:You hookup a fully charged battery and load resistor to the meter, enter the value of the resistor and the cutoff voltage and start a discharge cycle. The meter will switch on the load using a power mosfet and continiously measure the battery voltage. To precisily measure the voltage a reference diode is used. During the discharge you can select to display the current voltage and current or the time expired and capacity so-far. If the cutoff voltage is reached the load will be disconnected and the capacity will be shown on the LCD display.source

With this mAh meter you can check the mAh capacitance of your NiCad or NiMH rechargeable batteries.when you insert a freshly charged battery, the LED will start blinking and the counter
will start counting. After some time (1-3 hours) the battery is discharged and the counter will stop. The readout of the counter indicates the capacitance of the battery in mAh.source

This is a simple electro meter circuit.This circuit will detect electrostatic charge from the any material such plastic,comb etc.It can measure up to 30 cm from the target material.source