The rulers and matts have a width, how do you compensate for the width when you measure your fabric?

Do you place the edge to one side of the line or the other, or do you try to find the middle?

I usually use the outside of the lines. I don't think it really matters if you are consistent throughout the project.

Agreed.

Well yeah, it matters, and it can be different for each ruler depending on brand and age (years of cutting shaves the edges).

Measure with a fine line ruler or a piece of graph paper so you know what's accurate for the ruler you are using...and then use only that ruler for that particular project. Most of mine are accurate to the inside of the line, not the outside and there's almost a mm difference between the two.

I use the center of the line. And make sure your rotary cutter is perpendicular, not tipped or leaning one way or the other. Sewing accurately won't do much good if it's not cut accurately.

Agreed!

I recently got rid of my original 6 x 24 ruler because I realized over the yrs I'd shaved it down enough so I felt that it made a difference. I try to hit it mid line...

I was taught by my teacher that you should do it midline. You should also use the same ruler for the whole project because they aren't all alike. I only use the lines on the mat when I have a really large block that will be cut down when I'm finished with the design on it; other wise I don't use the lines on the mat when I want a precise measurement

Good idea.

This is one of the reasons I like the Creative Grids rulers, the lines are very thin.