Hello! Well this is a quite embarrassing problem but I think my maths has disappeared the last years. So I"m working on some calculations and i want to compare with the expermental data but there's a shift on energy that it has to be apply. So I thought I just need to to a simple calibration (experimental data vs calculated data and then a did a fit with origin where a get y= a+bx) Now if I'm doing this..its not like i'm just applying a shif of the same X number to everything (let's says i'm not doing shift= experimental data + X), so i'm changing the espectra. I guess I'm doing something wrong?