In my video "Photo Engraving on Slate with a Diode Laser"    • Photo Engraving on Slate with a Diode...   I talk about establishing your laser's dynamic range by using a grayscale test grid. A number of viewers reached out to me about how to create such a test grid.
This is a super quick video to show you how you can do this yourself in any graphics program.
Once you understand the limitations of your laser, the better you will be prepared to create better photo engravings on any material.