why miningpoolhub always shows less hashrate than i have?

2x GTX 970, miner shows 2042 kH/s, pool shows 1491kH/s
Ryzen 1600X, miner shows 450kH/s, pool shows 224kH/s
i5 7300HQ, miner shows 349kH/s, pool shows 93kH/s
GTX 1050, miner shows 495kH/s, pool shows 194kH/s

Im mining Zcoin