Dick's Waves

In his flight test reports Richard H. Johnson usually included an
assessment of the glider's wing condition.
He often sites 0.004" as being a acceptable degree of waviness. I'm
assuming this is wave height, but over what length?

The reason for asking, is I'm current having my wings refinished and I want
to determine how much of the spar shrinkage needs to be corrected.
I'm thinking that a flat spot in the wing profile can be tolerated as long
as the transition is gradual. The current distortion isn't too bad and
could most likely be fixed with a extra coat or 2 of gel confined to the
spar area. However, not sure thick gel is a good idea on an asw20 with
such flexible wings.

Thanks
David