This calibration card allows you to create a "table" to convert the inches of liquid measured on the Tank Tender gauge into gallons, if desired.
Particularly for rectangular or cube tanks, many users find just knowing the depth of fluid is adequate for their needs.

Boats and RVs are constructed with a wide variety of tank shapes and sizes. There are two main methods of converting the inches of fluid measured on the Tank Tender gauge into gallons for any particular tank.

1 - Choose a container with the incremental volume of liquid you desire for your calibration - 1 gallon, 2 gallons, 5 gallons, etc. Starting with an empty tank, use the container to fill the tank, recording the reading on the gauge with each addition.
For diesel tanks, the metered output on the fuel pump can be used to record the volume.
This method works especially well for tanks with non-standard shapes - such as V-berth tanks.

2 - Measure the length and width of the tank in 1" levels and calculate the number of cubic inches for each inch of tank height. There are 231 cubic inches in a gallon. Therefore, the number of cubic inches divided by 231 will give you the number of gallons per inch of tank height.

Each unique shaped tank will require a separate Calibration Card. Calibration Cards are usually mounted on the bulkhead right next to the Tank Tender Panel, if possible.