function startCalc(){
  interval = setInterval("calc()",1);
}
function calc(){
  one = document.calculator.input.value;
  two = document.calculator.number3.value; 
  three = document.calculator.totalcost.value; 
  document.calculator.subtotal.value = (one * 1) + (two * 1) + (three * 1);
}
function stopCalc(){
  clearInterval(interval);
}