its soley up to the discretion of the inspector, but most go by:

star chips with one leg longer than 2", a crack that goes from one end to the other, or you can move pieces of glass in relation to one another.

quick test: try to catch your fingernail on the crack. if you can, it will fail. if not, most of the time it will pass.

glass rules in the handbook are vague and contradictory, and our trooper in charge basically leaves it to the judgement of the tech.