# How to know the volume of gasoline used exactly based on the mileage of a truck?

We need to know how much gasoline cost we're incurring per trip for logistics, but we need to run experiments on how much gasoline is used for every unit of distance. (e.g. 15L/mile), but the issue, is the gauge we have is something like this:

We know how much gasoline we load in because gas stations have metrics, but how much of that is used is a little hard to get. With a gauge as shown in the image, the only way I can think of is to measure the length of the arc that increased after gasoline was pumped in the truck, then measure the length of the arc after the trip and then subtract the initial length to the length after the trip then use ratio and proportion to actually get how much gasoline was used for the trip.

Then I can also get the gasoline per liter by `[Gasoline Used in Trip/(End Mileage - Start Mileage)]`

I am wondering how accurate these gauges are and if my methods of ratio and proportion will work. I am also wondering if there are any tools to actually digitally show how much gas is used?