The old mechanical display gas pumps could only display prices between 0.0 and 99.9 cents per gallon. The workaround was to set the price per gallon to half of the sales price, then multiply the displayed total price by 2 to get the amount you owed the gas station. If you got 10 gallons of unleaded that was priced at $1.338, the meter on the pump would read a price 66.9¢ per gallon and a total of $6.69. When you paid that, $6.69 would be doubled to $13.38.
I remember that some stations in KC changed their pumps so that they metered gasoline by the quart, rather than by the gallon. And one enterprising station decided to try selling gasoline by the liter... That lasted less than a week!
Mark