How to calibrate D.C. shunt on

TUTORIAL FOR NEWBIES:

How does an ammeter work? Obviously you can't actually physically pass thousands of amperes of current through the rather small gauge wiring of an ammeter. So what you actually do is rely on Ohm's Law:
E = I x R
or as some people write it today
V = A x R

You cut out a short section of the bus bar and then jumper it with a block of copper or copper alloy precisely sized so that its resistance is very exact. We call this a shunt. Often its resistance is chosen such that when the rectifier is putting out its maximum power, the voltage drop across this shunt block will be 50 mV, and we call it a 50 mV shunt.

Say, for example, your rectifier is rated 5000 Amps. You adjust the dimensions of your shunt block so that its resistance is exactly
0.00001 Ohms because
.050 Volts = 5000 Amps x .00001 Ohms

So, when 5000 Amps is flowing, the voltage drop across the shunt due to its resistance will be 50 mV.
Now you simply wire a 50 mV voltmeter across the shunt but instead of labeling the scale 0 to 50 mV, you label it 0 to 5000 Amps.