"Bubble Level" phone app, free, get foil mounted in board, with board upside down on a stable surface, may need padding under tail, measure angle of foil box parallel to foil mast using the "flat edge" on phone, then note angle or zero level and measure rear wing angle "without" disturbing foil/board position. On AFS W95 foil rest phone on rear wing front screw recess to measure "relative" angle. You can also use calipers, by cutting a notch in each arm, so it locks on the front and rear edges of the wing, and then place phone on caliper shaft, that is more precise and an absolute measurement versus relative, just be careful to not move foil/board.
"Bubble Level" phone app, free, get foil mounted in board, with board upside down on a stable surface, may need padding under tail, measure angle of foil box parallel to foil mast using the "flat edge" on phone, then note angle or zero level and measure rear wing angle "without" disturbing foil/board position. On AFS W95 foil rest phone on rear wing front screw recess to measure "relative" angle. You can also use calipers, by cutting a notch in each arm, so it locks on the front and rear edges of the wing, and then place phone on caliper shaft, that is more precise and an absolute measurement versus relative, just be careful to not move foil/board.
I should have mentioned that I have a foil mast head shim that sets my foil fuselage at 0.0 degrees relative to the board bottom, that is why I can zero the bubble level app on my phone on the board bottom.