The highest contrast ratio of the Acer S230 is 100000000:1. That's over five times the contrast ratio of the most frequently found dynamic contrast ratio of 20000000:1.
This flatpanel monitor's contrast ratio (100000000:1) is in fact the best contrast ratio amongst all LCD screens of this age and type.
Amongst similar types of flatpanel monitor the worst contrast ratio is Mega Contrast.
There are a number of other PC screens that have a 100000000:1 dynamic contrast ratio currently available that you might want to consider including the H276HL ($199.99), or the 276HUL both from Acer which has a better Rating.