Avarage effective Hash rate on pool ( ETHERUM )

[N0pr3s3n7]

Hello , basically Im kind of new to mining and want to ask you guys about the difference between  
I am mining on eu.ethermine.org pool
reported hash rate by system (currently arround 330 mh/s )
avarage effective hash rate (based on shares last 24 hours - around 300 mh/s ).




Basically Im always getting arround 25-30 mh/s on avarage effective hash rate difference between real reported hash rate (my miners are hashing) . On the picture you see that it matches but it's because I recently switched one of the cards to mine other coin  , but after 24 hours I expect now to drop arround  300 -305 mh/s . I am getting on avarage arround 1-2 % stale shares , is this normal ?? Is this where the difference comes ? Also should I change the pool and be on other if the avarage effective hash rate matches better then Real reported hash rate ? Just feel like 1 of my cards is doing nothing because of this. Any opinions , share knowledge and statistics would be awesome , thanks in advance !

[coin123123]

pool calculate hashrate by accepted shares

your internet connection can affect shares not getting to the pool on time and lost

[vintagemintage]

reported hash means how fast the student tells the teacher he/she can finish the test
shares submitted per hour is how well they did on the test
effective/current hash is a recalculation of how fast they did test with the quality of their score (shares)
Average hash is an average of their effective hash over a time period (final mark in the class)