function startCalc(){
  interval = setInterval("calc()",1);
}
function calc(){
  one = document.autoSumForm.firstBox.value;
  two = document.autoSumForm.secondBox.value; 
  document.autoSumForm.thirdBox.value = (((one * 1) * (two * 5280 ) * 0.083));
}
function stopCalc(){
  clearInterval(interval);
}