dumb

Last time I use to play table tennis seriously I never noticed rubbers were labeled 1.7-1.9mm They were only 1.7mm or 1.9mm. Can someone please explain to me what it means if I am buying a rubber that is listed as 1.7-1.9mm. Both of my old rubbers flarestorm and flarestorm II have 1.9mm printed...

i'm sorry for the lame action I'm not just feeling well that day. Pls comment....