Calibration was made by adding 2.5 gallons at a time to an empty tanks
in a PA-22/20 tail dragger conversion on level ground.  Measurement 
from bottom of tank was made with a plastic tube (could have been a 
wooden dowel) held VERTICAL against the AFT EDGE of the filler opening.   
A mark was scribed on the plastic tube at each point with a file then 
marked with magic marker and the gallons for that point were written 
above the mark.  

Gals	Dist from Bottom
	    (Inches)

5.0		0.250
	
7.5		1.187
	
10.0		2.062
	
12.5		3.062
	
15.0		4.250
	
Full		6.500