Review on Starrett C637E 150 Millimeter Graduations Thickness by Adam Tidd

I have recently purchased the Starrett C635-1000 series and C635-500 series. When the 500mm ruler is placed next to the 1000mm ruler I notice that the 500mm ruler is significantly 1/2mm smaller than the 500mm mark on the 1000mm ruler. It seems to me that this is a large variation, but perhaps this variation is within the tolerances of the manufacturing process. Perhaps my expectations for Starrett were unrealistically high, but oddly I'm now in a worse position than without a 500mm or 1000mm ruler because I don't know which to believe now!