I noticed my payouts were a bit low and with the reward halving I went on the site and found that my current rate was 2100 Mhash and the history shows 1900 Mhash for the last 15+ days.
Your miner doesn't actually report the hashrate to the pool server. Pool servers try to guess your hashrate based on how many proofs of work ("shares") you send in. When you are lucky and find many, the pool will show a higher than actual hashrate, and the opposite when you are unlucky. So the hashrates shown on pool web servers are just guesstimates.
I guess your actual hashrate is 1900 Mh/s and the inaccurate website hashrate just showed 2100 for a short time while you were being lucky and finding many proofs of work? Or what hashrate does the miner software on your computer show?
