Sorry for n00b question but is there an index like sensex or Nifty that includes the sum total of the entire stock market?

Can anyone please explain the margin thing

zerodha always report less margin in funds tab, but don’t let me take more position by stating required margin error

From last few days what I am doing is
I check margin on opstra and other sites, then take position on zerodha accordingly
zerodha still show less margin in used tab, and show more funds in available margin
But this time I understands that margin requirement in rejection error is same as what other sites are reporting

There seems to be error in reporting margin in funds tab but zerodha’s RMS system is calculating correct margin and hence not letting me take more positions

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