Question about mining pool

[skullkid]

This is probably a relatively noob question, but I set up mining on my 9800GTX+ recently on slush's mining pool (https://mining.bitcoin.cz/) and I'm getting around 30 Mh/s. My question is when I look at the estimated reward, why does the amount keep fluctuating? Is this intentional, and how does it work then? Also, how long would it take to get about .5 BTC with my video card? Thanks for the help.

[nmat]

It fluctuates until a block is found. There is no way to know when that will happen so the estimated reward is just that, an estimation. With that card running 24/7 it will take you about 1 month to get 0.5BTC. See here: http://tpbitcalc.appspot.com