Need some insights regarding Shunts for ammeters
The best answer is to get a real multimeter.  You really shouldn't expect something that costs $3.35 to do what even a mediocre $20 multimeter can do.

However, to answer your question, a shunt is just a resistor.  Resistors are current to voltage converters by Ohms law:

&nbsp;&nbsp;Volts = Amps * Ohms

Of course there is a tradeoff here.  Generally you want a measurement to perturb whatever you're measuring as little as possible.  In this case, the voltage across the shunt is voltage taken away from the device.  You make the resistance low to minimize this voltage.  On the other hand, too low a voltage is hard to measure accurately or with little noise.

Most ordinary ammeters select a shunt that causes about 100 mV for whatever the full scale current is.  That's not too hard to measure with three digits of accuracy, especially when you get the user to manually adjust the zero offset for you.

At large currents like 100 A, a different technique is usually used.  This is because with the shunt adjusted to about the same resulting voltage, the power the shunt must dissipate is proportional to the voltage.  100 A at 100 mV is 10 W.  That would require a deliberate power resistor, and you then have to worry about the resistance change over temperature.

Large currents cause enough of a magnetic field around them that it becomes feasible to measure that instead of trying to cause a deliberate voltage drop.  High current meters therefore are usually just a fat wire with a Hall affect sensor nearby.  It's unlikely that's what's in your $3.35 meter, though.