I haven’t found any direct way to “shift” the histogram’s “bin contents” so I’d like to propose the following extensions:
// this = this + c1h1 + c2
void TH1::Add(const TH1 h1, Double_t c1 = 1, Double_t c2 = 0)
// this = c1h1 + c2h2 + c3
void Add(const TH1* h, const TH1* h2, Double_t c1 = 1, Double_t c2 = 1, Double_t c3 = 0)
These changes should be fully “backwards compatible”.