Graph Grid gives you windows with grids in actual real world inches or centimeters. Move them around your space to have a see-thru grid over whatever you want.
Some ideas for how to use them:
* Measure objects near or far by putting the window right on them
* Use the grid windows as an easy level to arrange multiple picture frames
* Lay a window flat or on an easel to help with drawing and painting
* Grid Method -- arrange a grid window on your canvas or sketch paper and another grid on your subject
* Conversions - arrange an inch scale window and a centimeter scale window to do visual conversions between units.