You cannot compare hashrate reported by the pool so precisely.
It is calculated with the actual shares that you send.
Therefore, it vary depending on the day you mine, the difficulty, the number of miners, the pool hashrate, network congestion, the latency, luck factor, and so on...
Better run your own tests... Lots of smart words put in one sentence but have no meaning all together.
Hashrate reported by the pool is calculated with the shares you send -> not precise.
Hashrate reported by the miner -> real hashrate (if you trust the dev)
There... less smart words. Do you understand?