I, too, have been advised to always use the same ruler throughout a project and advise that myself. While I've not checked mine ruler to ruler, I would not be surprised at any discrepancies. I have a small, 6x3.5 ruler that I really like for trimming small pieces. It is a brand not of any others that I had. Recently bought the same manufacturer's 6x24 for that very reason. Doesn't have 1/8" marks though but since I rarely use them, decided it wasn't a major factor. And except for very large cuts, don't measure using my mat. If I do have a large enough cut that I need to measure with the mat, I usually cut about 1/4" larger and trim up the smaller sub cuts.