intensity 1

The previous short post shows where the reflexions are at the 2theta position.

but how strong is it?

then we need consider the contribution of every single atoms, what elements (how much an atom can scatter the photons) and what position (what a phase angle difference it can cause) can tell us how strong it is. 

 

add all of then together, you'll have something very closely related to the theoretical intensity value.  (sorry, one of the i's is for the root of -1; the other i's are indices)；