A professional from California says:
May 3, 2016
Have you installed screens using this guide for the "B" type door? I've always deducted 1/4", not added 1/8". Even deducting 1/4" the door is often too tall.
Dave from SWISCO responded:
May 4, 2016
Hello! Always good to hear from you. Are you referring to the "B" measurements for the "U" type door? If so, what we would do would be to deduct 1/8" from the tightest measurement of the track, measuring in three places: each end and in the middle.