Literally speaking, a Kasauti is a small piece of stone which is used by Goldsmiths for the purpose of testing the quality of gold. They simply rub the gold on this Kasauti and after seeing the impression of gold on it, they decide as to what is the extent of purity of the gold. Thus this is a test for gold and in a physical sense, Kasauti is known as a Touchstone.

But this is generally used in a figurative context. Please have a look at the following sentence:

Wo hamaari *Kasauti* par khara nahiN utra.

Here it means that the person did not live upto expectations and he failed to accompalish the job which he was supposed to do. He just failed in the test.

Hence Kasauti is a touchstone, assay, test, proof.

Hope this helps.