I have seen that in X-ray astronomy, astronomers often talk in terms of photon index $\Gamma$, which is related to spectral index $\alpha$ by relation $\Gamma$ = $\alpha$ + 1. Are the errors on $\alpha$ same as the errors on $\Gamma$? Someone told me that there is some kind of scaling relation so that percentage error of photon index and spectral index are same. You cannot directly take error of photon index to be the error of the spectral index. From the mathematical relation between these quantities, I think the errors should be the same. I am confused. Can someone help me?