VERY unscientific....
4 13/16"
I rotated my crank till it was on TDC on the 67 pointer.
I marked the damper at the 0 on the 70 up pointer.
I put some masking tape around the damper and marked the two TDC marks (should have done that first)
I took the tape off and laid it out flat and measured.
NOT accurate enough to scribe your damper but gets it in the ballpark