Here comes the most critical step: measuring the window panes. Not too difficult but very critical. In essence you have to measure all four sides and assess whether the window pane is straight or not (some are not straight by construction, but often they are not 100% straight because they are hand made). The process becomes painstaking if you have a total of 47 window panes! In addition to the instructions from Optoglas, I have used a professional laser meter (Bosch DLE70) for accurate measurements and I have developed a few tricks along the way to double check my measures (too technical and tedious to describe here, but drop me a line if you want to know more).
To make a long story short, when you are ready you send the measured window sizes to Optoglas, they send you back the corresponding glass sizes for confirmation (some minor adjustments are sometimes necessary) and then you keep your fingers crossed and hope that you did not make mistakes and that.... the the road to your place is not too bumpy for the truck carrying your precious new glasses .... ;)