It's not as simple as that. For one thing, there is a wide range of different screens used to display text, and each screen may exaggerate or reduce contrast to

It's not as simple as that. For one thing, there is a wide range of different screens used to display text, and each screen may exaggerate or reduce contrast to a different degree. It's also important to remember that very high contrast such as pure black on pure white can cause serious problems for dyslexic readers.