Short selling help

Please help me with calculating my short selling trade(NIFTY SPOT), i havent done short selling till date, wanna try my hands on, i am trying to understand the zerodha calculator here, i have shorted 8300CE AND 7700PE 2 lots each of dec expiry, Margin showing here is very much above my expectation, i want to know what does the span and margin exposure means here, also premium receivable is 13613 here, is that the premium i will receive if nifty expire in between 8300 and 7700? please let me know

please refer the below image for reference

http://ift.tt/2gbmdKN

Short selling help