There are only two methods that I know of; One IIRC uses a length of grass or leaf and if the keris fits the sum of the lengths used to measure it then it is a good keris.
The other is done by measuring using the distance between a part of the thumb (Knuckle to tip?) and repeating a mantra with every thumb length measured.
How the results are determined I don't know but I would speculate that a good keris has an odd numbered sum of each form of measurement.
