Why "cut on the left"?

Here's what I think this is about. As a new quilter I tried to learn from reading a pattern and doing things I thought made sense. I started cutting my fabric by using the markings on my MAT. Therefore I would square up my fabric by lining up the bottom on a line on my mat then cutting the right edge off by lining up my ruler with markings above and below the fabric to make a straight edge. Then I would use the lines on my MAT (what I could see above and below the fabric) and move my ruler from right to left and cutting the strip that was OUTSIDE of the ruler, to the right of the ruler. Now I've learned to more accurately cut you should measure with the RULER over the fabric and the strip size you want lays UNDER the ruler. So you square up the left edge of the fabric by placing your ruler on top of the fabric, measuring what's UNDER the ruller with the markings on the ruler, then move the ruler left to right as you continue to cut your strips. So the strip size you are cutting is always underneath the ruler. Did that help at all???

Well, I don't know if it help them but it sure did help me! Thanks!

I've got it now. Thanks for all of the input!

Haha! This kind of thing is so hard to describe in words. I think we need a tutorial!
Jenny.....???

denmck is right on the money. I was orginally taught to use the lines on my MAT to cut my strips and quickly found this to be frustrating as many of my strips didn't come out right. I figured out on my own to use the lines on my RULER as they were more accurate than the lines in my MAT. Another quilt teacher confirmed this with me and said this is how she teaches.

I am left handed and cut to the right edge of my fabric with my ruler laying on top of the fabric. If I were right handed and using this technique, I would cut on the left edge of my fabric.