Throat guage What do the numbers mean?

I am going to look at a rifle that guages 3. I ume this is erosion in the chamber, but what exactly does it mean? Is 1 the best? How good is a rifle that guages 3 It is an older m1 garand that is supposed to be "like new". I would be very leary, but it is one that a trusted friend told me about that came into a store where he works. (he does not get a commission or anything like that)