Install screentest by entering the following commands in the terminal:
sudo apt update sudo apt install screentest
Description:
Utility to test the quality of screens
Screentest is a CRT and LCD screen testing utility. Ever wondered how good the quality (sharpness, linearity, convergence, etc.) of your CRT/LCD monitor is? Screentest displays the testing patterns which you can use to evaluate the quality of your monitor.
Homepage: http://screentest.sourceforge.net/
Version: 2.0-2.2build1
Section: universe/utils