In my steel book it says 1 MM dec. equivalent is .0394 when I x that x 100 I come up with 3.94 but the book says 100 MM is actually 3.937

The decimal equivalent for 100 MM is 3.937 so when I devide that x 100 I get .03937

If I take .03937 x say 78 MM I come up with 3.07086 but the book says its actually 3.0709

What am I missing.