In order to place my AOA (Angle of Attack) ports, I needed to determine the wing chord. That is the front-to-back distance from the leading edge to the very back tip of the aileron or flap (depending on where you are measuring). After you determine the chord, you then figure 15% to 40% of that, and you have the range for port placement. In my case, I measured the chord about 150mm inboard of RR9 where it is 1470mm, placing the 15% location at 220mm and the 40% at 588mm. Given that range, I selected 255mm (17.3%) back from the leading edge, which is about 90mm ahead of the main spar rivet line (on the top of the wing). This allows room for the tubing coming from the upper port to have a short section that goes uphill, as specified in the plans.