I use my marked ruler to measure the fabric from the right edge (I am right handed). I then put my Slide Lock ruler right up next to the ruler to the left and cut. The portion being cut off is the measured strip or square. So just like you and Jan, except I use the Slide Lock for the cutting instead of an additional marked ruler.

Excellent tip. I admit I do have problems with the ruler sliding. I will try this next time I do some cutting.