You probably already know this, but...
If like me you have a V-power card and put 30+ litres in a week and want to use claim their 200extra bonus points for 6x15litre fill ups in March/April vouchers... you can put 15 litres in, put the pump down, leave for 10seconds, pick up and put another 15 litres in as the pump will store 2 uses in any one time, go in and pay for them as two seperate transactions, swiping your v-power card each time....
Thus achieving 8 x15litre fill ups instead on 4x30litre fill ups which wouldn't achieve the 6x15litre bonus points...
HTH,
Dom