That's one of the reasons I stick mainly to one brand of rulers (Creative Grids), though the Block-Loc's work with them.

I make wine, and have found that the gallon and or imperial gallon marks on the buckets and carboys (the imperial gallon and american gallon are quite different also) mean nothing! I always have to use my usual gallon container and remark all the lines. I think the same is true for rulers. It depends on where they are manufactured, and whether they really care about precision. I am fortunate that my cutting mats are very accurate, so that is what I use for my measurements.
Phyllis

ARGH why has no one ever told me this......I had no idea...I will change the way I do things from now on! Thank you for opening my eyes!

I guess I'm another one of the lucky ones. I have one O'Lipfa and several OmniGrids and they match up. Even checked against my mat both brands match up with it, too, although I don't use it for exact measuring. Could it depend on the day of the week rulers are made, like automobiles? They say don't buy a car made on a Monday or a Friday:).

JMHO..All Hail the wonderful, informative Quilting Board!! I Love you all and everything you teach us!

I learned this the hard way also. Don't forget to check your measuring tapes (yes, I still use one occasionally). My measuring tape and cutting mat were way way off. I now use omnigrid and have had much fewer problems.

I noticed this a l-o-n-g time ago and wrote to all the companies, asking them why they don't all have the same 1 inch measure on their rulers. No one ever answered my letters! The big mat on my cutting table is fine for the first 30 inches, but it stretches the inches after that! Go figure! At least I know that, and don't rely on the mat at the far end.

OH, My! My quilts must be awfully out of shape...my eyes are so bad that I can't even see the individual threads when I'm cutting! :D Luckily, my target audience (grands and children in foster care) doesn't care about that stuff.