The highest contrast ratio of the Acer S242HL is 100000000:1. That's over five times the contrast ratio of the most common dynamic contrast ratio of 20000000:1.
This PC display's contrast ratio (100000000:1) is in fact the best contrast ratio across all similar spec PC monitors that have been available for more than two years.
The worst contrast ratio amongst similar types of PC display is Mega Contrast.
There are a number of alternative LCD screens that have a 100000000:1 dynamic contrast ratio currently available that you might want to consider including the 276HUL (£362.40), or the H276HL both from Acer which has a better Rating.