Pilotfighter, most flat bottom wings are of the semi type like in Paul's drawing. (thanks Paul) This is a modified flat bottom wing that has a rounded leading edge, called a "Phillips entry". This causes the chord line not to be parallel to the flat bottom line.

A true flat bottom wing has no rounded leading edge, but a totally flat bottom right up to the leading edge. The incidence meter should then clamp on parallel to the flat bottom I think.

Ernie