B.N.Rathi margin calculator is a tool, it enables you to compute total margin requirement before entering in to a trade and also indicates the spread benefit for the hedged strategies. it is computed based on mae developed logic and covering equity derivative, commodity and currency segment.
it is recommended that for an accurate srpead benefit calculation, one should do the calculation for the single scrip and do not mix up with other markets. like adding stock futures + stock options (multiple leg) + commodity derivative.