function workSaving() {

  var mpg = document.calc.mpg.value;
  var yearlyMilage = document.calc.yearlyMilage.value;
  var petrolCost = document.calc.petrolCost.value;
  var lpgCost = document.calc.lpgCost.value;
  var conversionCost = document.calc.conversionCost.options[document.calc.conversionCost.selectedIndex].value;
  var tankSize = 60;
 
  var yearlySaving = ((yearlyMilage/(mpg/4.546))*petrolCost/100)-((yearlyMilage/(mpg*0.95/4.546))*lpgCost/100);
  
  var ROI = conversionCost/(yearlySaving/12);
  var lpgGallon = lpgCost*0.045461;
  var petrolGallon = petrolCost*0.045461;
  var runPetrol = (petrolCost*4.5461)/mpg;
  var runLPG = (lpgCost*4.5461)/(mpg*0.95);
  var tankMiles = (((tankSize/4.5461)*mpg)*80)/100;
  
  document.calc.lpgGallon.value = lpgGallon.toFixed(2);
  document.calc.petrolGallon.value = petrolGallon.toFixed(2);
  document.calc.runPetrol.value = runPetrol.toFixed(0);
  document.calc.runLPG.value = runLPG.toFixed(0);
  document.getElementById("yearlySaving").innerHTML= "£ " + yearlySaving.toFixed(2);
  document.getElementById("ROI").innerHTML= ROI.toFixed(0) + " months";
  //document.calc.tankMiles.value = tankMiles.toFixed(0);
  
}