Remove the filler cap from one of the fuel tanks. Insert the paint stirring stick into the tank until the end of the stick touches the bottom of the tank. Use the permanent marker to mark the stick where it meets the inside top of the tank. Remove the stick from the tank and replace the filler cap.
Measure the distance from the bottom of the stick to the top marking. Divide this measurement by two, and mark the stick with a horizontal line halfway between the top marking and the bottom of the stick. For example, if the distance between the bottom of the stick and the top marking is five inches, mark the stick with a horizontal line 2.5 inches from the bottom of the stick.
Check the Pilot’s Operating Handbook to determine how many gallons of fuel the tank holds, and how much of that fuel is unusable. Write the usable fuel amount above the top line. For example, if a standard 21.5-gallon tank contains 1.5 gallons of unusable fuel, write “20 gallons” over the top line.
Divide the total usable fuel rating by two and write this number over the horizontal line that is between the bottom of the stick and the top line. For example, a standard tank holds 20 gallons of usable fuel; therefore you would write “10 gallons” over the top of this line.
