I do all my bridle lines in pairs, same one for each side and check both are the same length.

Firstly I make a loop on the end of the line on the reel, I make the loop 12cm long with 2cm at the end unsewn:

Marked out:

First loop complete, then I measure the bridle length (plus 12cm for the other loop) and cut:

First brake secondary pair finished:

And attached straight on to kite (to prevent any mix-ups!)