Add, Divide and multiply TH1 with the root context menu

I would like to use the widget that appear when I call Add, Divide or Multiply from the context menu of a histogram, but I’m not able to understand what I have to insert into the box that should contains the histogram pointers.
For example, I have created two histogram in two different canvases

TH1D * h1 = new TH1D(“h”, “h”, 100, 0, 100)
TH1D * b1 = new TH1D(“b”, “b”, 100, 0, 100)

I have tried to select Add from the contextual menu of the h1 and insert the value h1 and b1, or the name of the histogram h and b without result.

Thank you very much for your help.

Best regards
Andrea Bulgarelli

This will work only if the histograms are in the same directory and canvas.