Ｃａｎ one ｓｕｂｓｔｒａｃｔ ｏｎｅ ｈｉｓｔｏｇｒａｍ ｂｙ ａｎｏｔｈｅｒ ｈｉｓｏｇｒａｍ？

[brentsun]

I have found a previous post, attached blow:

Substract two histograms in different root file

Hi, I’m trying to subtract two histogram which have the same name in two different root file. Is there any idea? Thanks.