How to set the minimum value of a histogram to zero

Hii rooters,
I have three different histograms of some analysis. (The difference in their magnitudes is large.) Now I want to compare them in one histogram. So I superimposed them in one histogram. But the problem is they are nowhere near to each other as shown in picture attached.
I want to set them to start at one level of the Y-Axis. So that comparison can be made. How can it be made? I tried SetMinimum(0) . But it is setting the starting point of Y-Axis to zero for all three histograms but distance between them remains same. I want to set individual histograms to zero in one superimposed histogram. ( i have attched snippet of the macro)


signal1D2->Scale(1. / signal1D2->GetBinContent(1)); // (1) or maybe better (2)
signal1D3->Scale(1. / signal1D3->GetBinContent(1)); // (1) or maybe better (2)
signal1D4->Scale(1. / signal1D4->GetBinContent(1)); // (1) or maybe better (2)


signal1D2->Scale(1. / signal1D2->Integral());
signal1D3->Scale(1. / signal1D3->Integral());
signal1D4->Scale(1. / signal1D4->Integral());


signal1D2->Scale(1. / signal1D2->GetEntries());
signal1D3->Scale(1. / signal1D3->GetEntries());
signal1D4->Scale(1. / signal1D4->GetEntries());

Thanks Wile . It worked !!!

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