I am curious about a question. in synchrotron station,people use x ray to do kinds of experiments. They use the x ray ,how do they know the characteristic(like wavelength,brightness) of the ray they use. Does they measure the x ray when they use it simultaneously? Does this have an bad effect on the stability of the x ray? if they characterization before application,is this too troublesome? how they actually change between characterization and application? Thank you!!