Make the window as large as possible, display the grid for up to 10 minutes, and then switch to gray. Screens with image retention will show a faint impression of the grid on the gray background.
By using this, you agree that I AM NOT RESPONSIBLE for any damage you may incur.

Look away during the test so your eyes don't get fooled at the end.

If this proves useful to you, I'd love if you tried Overcast. Thanks.