What is the criteria for deciding MIS margin percentages

what are the criterian for deciding MIS for equty and futures?
I have found out that for the same scrip either for Equity BO/CO or Future BO/CO the margin range is very very less or very very high.
Sometimes the brokerage calculator doesn,t work properly.It shows very high brokerage value, but after refreshing it shows the right amount.

Criteria for determining leverages is the volatility and liquidity in a scrip. Yeah sometimes equity and futures leverage might vary.

Brokerage calculator seems to be working fine. If you find this happening the next time, can you email a screenshot to [email protected]