Dave

The vehicles in question are buses with large tanks that do relatively small
mileages. I also need to monitor the MPG per trip rather than an overall
figure.

Terry

"Dave" wrote in message
...
Hi Terry,
For mpg calculations, you don't really need to consider whether the tank
was
full when you started, unless you have a very small sample of data.
All you really need is total miles divided by total gallons. Each time you
put petrol in, whether you fill it or not, just record the gallons and the
miles. The more miles and gallons you record, the less it will matter what
state of fill the tank was in when you began.
Regards - Dave.