The simplest technique consists in weighting
the intensity by hand.

Peaks were cutted out of the paper drawing, by chisel, and then the weight of the pieces of paper were measured, with a balance.

The peak surfaces were carefully measured by a planimeter.

You can really solve simple problem by these methods.

Nowadays, serious pieces of work are undertaken by whole profile analysis.

Two approaches  make use or not of the cell parameters as a constraint for prediction of the angular reflection positions.