Just choose the shape (dots, lines, squares, or even hexagons), move the slider to adjust the spacing, and print away. The ruler at the top (which I believe is in centimeters) helps with the sizing.

Reader Marty Zager writes in: There have been so many times that I'm scrambling around to find a ruler to measure something in my office or apartment, and I'm completely sans ruler.

You can measure most things in the physical world with centimeters ... standard ruler handles both---but it ignores digital environments, which render in pixels, and typefaces, which print in ...