Article copyright D. S. Brown, except for the image which is copyright Rand McNally 1975.

Many modern cars have trip computers which give you a readout of your gas mileage. For those of you who have older cars, or who wish to directly check the mileage for themselves the procedure is simple.

Completely fill up your tank each time you get gas and write the mileage from your odometer on the receipt that comes out of the pump. Taking a few receipts in a row, the mileage tells you how far you went between fill ups. The pump receipt lists how much gas you put in. Some prefer to record the mileage and amount of gas in a log book.

True fanatics will want to go to the same pump at the same gas station to ensure that the car sits on the same angle each fill up and that the 'shut off' happens at the same point. To be completely exact, you need the same load distribution in the car, too. If you have a passenger and items in the trunk, and next time you don't, the angle of the gas tank changes which can distort tank 'full' point.

For most of us, just writing down fill ups is close enough. Take the current mileage; subtract the previous mileage to determine how far you went between fills. Take the distance in miles and divide by gallons to fill up and this gives you MPG.

Canadian and European readers can convert this figure to L/100k by googling 'conversion' and finding an online site to convert MPG to metric.

Below is a little MPG 'computer' printed on the back of a Rand McNally 1975 San Francisco, CA map.