Different plot with zoom

[alberto.paniate]

I have to fit these dates with a sine. The plot is ok and I obtain a good chi square. But I see this:

This is so strange but when i zoom it for example between 15 and 40 (where the fit is not good according to this picture) I obtain:

that agrees with the chi sqare

why?

[Wile_E_Coyote]

Try:

your_fit_function->SetNpx(1000); // or even 10000, if you like