Ok, using this handy tool; Right triangle calculator
, I did some estimating.
As built, the wing (measured with opposite panel flat and from root to the bottom of the last rib) has only about 1". The length of the panel from root to last rib is 16.75". Plugging these into the handy-dandy calculator yeilds 3.42deg which, of course has to be divided by two since the opposite panel is flat, yeilds only 1.71 deg. Way too small.
Looking at some other plans that I have, the dihedral angle looks to be between 4 and 6 degrees (where did I leave my protractor). So, given that range, it looks as though the measurement, performed as above, at the tip rib would be between 2.34" and 3.52". Splitting the difference results in 2.93. Erring on the side of caution, rounding up would seem to make sense, so 3" is the final number.
Now reversing the process to check the angle results in 5.14 degrees of dihedral. So now the question is whether 5 degrees sounds reasonable.