I am trying to measure for replacement windows in a wood frame wall of the house. So, I believe the replacement windows have a nailing flange. I have taken apart the inside trim and measured the existing windows from the inside, but cannot get to the outside becaue it is on the second story of the house and also has trim boards covering the actual edges of the window anyway. Can someone tell me if the “tip-to-tip” measurement is different from the interior measurement and the exterior measurement? From what I can tell this window is about 1/2 inch bigger if I were to measure it from the outside of the house, instead of measuring it from the inside of the house. Thank you so much for any help. I really appreciate it.