Good Evening,
Ideally you don't have to do the breakout/breakdown calculation manually.
Once you insert the values on this link
http://www.pivottrading.co.in/pages/breakout.php
It will automatically give you the intraday breakout & breakdown levels.
Rule :-
Buy Above/at the breakout levels(only & only if the level is sustained for 10 mins.)
Sell Below/at the breakdown levels (only & only if the level is sustained for 10 mins.)
My personal trade is OTD(one trade per day) where I blend these levels with the Options DELTA values & go for Naked CE & PE(without any fear).
Only in the last week of expiry I execute my OTD trade in nifty futures coz of the Time decay factor in Options.
Thanks!