Before you start making the shuntand it is necessary to measure the internal resistance of a dial indicator. Use ordinary tester or multimeter (either dial or digital). In this case, it is necessary that the current through the test device was not too large, otherwise the arrow may be deformed.
Now calculate the voltage that should be provided to the indicator that the arrow has deviated completely. For this, set the full deflection current in amperes and the measured resistance of the device in ohms. Then substitute them into the standard formula of Ohm's law:U=IR where U is the voltage required for full deflection, and I is the current full deflection, R is the measured resistance of the frames.Do not be surprised that calculated according to this formula, the voltage will be very small.
Now you need to calculate the resistance of the shunt. It will be so small compared to the resistance of frames that the latter can be neglected. Resistance shuntshould be such that when passing current through it, which is of the ammeter limit, the shunte fell a voltage equal to the calculated in the previous formula. Thus, this resistance may also be calculated by the standard formula of Ohm's law, but modified in the following way:R=U/I, where R is the required resistance of the shuntand, U - naprijenie full deflection of the indicator calculated by the previous formula, I is the limiting current, the measurement of which will be calculated your ammeter (if it is expressed in milliamperes, put it in pre-amps).
Correctly connect between the indicator and the shunt. Namely himself , the shunt will engage directly in the circuit, the current in which is to be measured, and indicator connect the wires to it. Thou to do the opposite, turning on an led indicator in the circuit, and a shunt connecting the wires to the indicator, the latter will explode or even burn. Think about why.
Manufacture for microammeter new scale having graduations in milliamperes or amps and the corresponding scale.