The highest contrast ratio of the HP ZR24w is 3000:1. That's 100% less contrast ratio than the most frequently found dynamic contrast ratio of 20000000:1. The best contrast ratio of all medium monitors that were launched more than two years ago is 100000000:1 and the worst is Mega Contrast.
Alternative flatpanel monitors that have a 3000:1 dynamic contrast ratio currently available which you might also want to consider include the Benq BL2410 (£172.11), or the Asus MK241 which has a better Rating.
If the contrast ratio of this HP PC screen is not high enough for you then you might want to consider the EA224WMi (£127.14) (25000:1), or the MultiSync EA244WMI (£336.00) (25000:1) both from NEC which also has a higher rating.