I'm suprised so many posts in favor of the meter. I tossed my mine years ago and use the distance method as described by R8893. It's more accurate assuming you have a flat level board, a good quality triangle. Calculate the inverse sine of the difference in height divided by the wings chord to get the incidence angle in degrees. No sticky meters, no $6 batteries, etc.

Height l.e. - Height t.e. = chord x sine (degrees of incidence)

Degrees of incidence = sine(-1) [(Hl.e. - Ht.e.) / chord]