So I decided to work on this quilt pattern today
http://delawarequilts.com/BOMs/AlpineCross/index.html , and ladies and gentlemen, I have a really stupid question .... I have like 5 quilting rulers.... and I have NO idea how to measure a 3 3/8" square. None of my rulers have that marking, or if it does... I don't know how to read it

.... Can anyone help me out?
Thanks in Advance
Mary Jo