The most tried and true method SWIM
knows which doesn't require anything fancy is the burn test method.
The test basically involves counting how many seconds it takes for the meth
to re-crystallize after it has been melted to liquid form.
2-3 Seconds means good quality
5-8 Seconds is average
Anything above 10 seconds is inferior product.
SWIM recommends using a jet lighter as it is able to heat up the entire portion of your meth simultaneously.
Therefore if you do see some parts re-crystallizing before the other, you are able to gauge as well, how much of your product has been mixed.