How to calculate error in ROOT

Hi,

This simple blog explains why the bin error for weighted histogram is equal to the square root of their the sum of the bin weight square.

https://www-zeuthen.desy.de/~wischnew/amanda/discussion/wgterror/working.html

Another derivation is also here

http://www.hep.uiuc.edu/e687/memos/weight_err.ps

Lorenzo