Finding an accurate high current source is the trick.

It doesn't need to be that accurate, and it doesn't need to be super-high. You can use a moderate current, and just measure it accurately.

 

I used to measure cable resistance (to check that it was really copper and had the correct cross sectional area)
I used a fixed voltage power supply and a power resistor which I had previously measured accurately. The power resistor in question was my audio dummy load.

 

Finding an accurate high current source is the trick.

All you need is accurate measurements of Volts and Amps. So any power supply including a small battery in a pinch.

 

You'd be surprised!
A 60mV/60A shunt has a resistance of 1m ohm.
You only need 1.2uH of inductance to be 10% out at 60Hz.

To be perfectly pedantic, it won't be a different resistance, it will be a different impedance.

Interesting. I haven't come across inductance in spec sheets for current shunts.

These sell for $100+ a piece: https://riedon.com/media/pdf/RSJ.pdf

It does say "Non-inductive Metal Element". So no inductance at any frequency?