var compression_calc = function () {
  var bore, stroke, hv, pv, gasket, cylinderv, gasketv, cr;
  bore = Math.pow((Number(document.cr.Bore.value) / 2),2) * Math.PI;
  stroke = Number(document.cr.Stroke.value);
  hv = Number(document.cr.HV.value);
  pv = Number(document.cr.PV.value);
  gasket = Number(document.cr.Gasket.value);
  cylinderv = Math.round(((bore * stroke) / 1000) * 100) / 100;
  gasketv = Math.round(((bore * gasket) / 1000) *100) / 100;
  cr = Math.round(((cylinderv + hv + pv + gasketv) / (hv + pv + gasketv)) * 100) / 100;
  document.cr.CylinderV.value = cylinderv;
  document.cr.GasketV.value = gasketv;
  document.cr.Compression.value = cr;
  return cr;
};