This chart is from jan 2010 onwards. The trendline support comes to 4876 for the day - current week's S1 - break of which would lead to 4777 - 38.2% retr of the move from 4786 - 6338.
Trading above the Day pivot of 4985 would give some strength for intraday.
Owing to weak global markets NS is likely to gap down and if supported at the trendline at 4876, then the fibo retracement to be watched from 5077 - 4876 would be,
23.6% = 4938,
38.2% = 4965
50% = 4985 - coincides with day Pivot.
