What is the siginificance of the number 1,2,3,4 marked on the two edges of both sides of shaving blade?

Question

This refres to the ordinary shaving blades avaialable in the market

Answer 1

To ensure uniform usage of all the edges. If you save with edge marked on the first day, then use the edge two one the next; like that go on rotating the blade. After four days, you can start second cycle of usage. This way you get a smoother and uniform shave on all days.

Answer 2

To maintain the order of usage. Use one No. once, in that order you can continue.