function change_size_unit2(n,c){
  var ft2r = 10.7639;
  var m2r = 1;
  var pingr = 0.3025;
  var v = document.getElementById(n+'_o').value;
  if(c == 'ft2'){
    document.getElementById(n+'_d').innerHTML = Number(v*ft2r).format('0,000.00');
  }else if(c == 'm2'){
    document.getElementById(n+'_d').innerHTML = Number(v*m2r).format('0,000.00');
  }else if(c == 'ping'){
    document.getElementById(n+'_d').innerHTML = Number(v*pingr).format('0,000.00');
  }
  
}

function change_size_unit(n){
  var ft2r = 10.7639;
  var m2r = 1;
  var pingr = 0.3025;
  var c = document.getElementById(n+'_m').value;
  var v = document.getElementById(n+'_o').value;
  if(c == 'ft2'){
    document.getElementById(n+'_d').innerHTML = Number(v*ft2r).format('0,000.00');
  }else if(c == 'm2'){
    document.getElementById(n+'_d').innerHTML = Number(v*m2r).format('0,000.00');
  }else if(c == 'ping'){
    document.getElementById(n+'_d').innerHTML = Number(v*pingr).format('0,000.00');
  }
  
}

function isType(o,t) {    return (typeof o).indexOf(t.charAt(0).toLowerCase()) === 0;}

/**
 * Formats the number according to the 'format' string; adherses to the american number standard where a comma is inserted after every 3 digits.
 *  note: there should be only 1 contiguous number in the format, where a number consists of digits, period, and commas
 *        any other characters can be wrapped around this number, including '$', '%', or text
 *        examples (123456.789):
 *          '0' - (123456) show only digits, no precision
 *          '0.00' - (123456.78) show only digits, 2 precision
 *          '0.0000' - (123456.7890) show only digits, 4 precision
 *          '0,000' - (123,456) show comma and digits, no precision
 *          '0,000.00' - (123,456.78) show comma and digits, 2 precision
 *          '0,0.00' - (123,456.78) shortcut method, show comma and digits, 2 precision
 *
 * @method format
 * @param format {string} the way you would like to format this text
 * @return {string} the formatted number
 * @public
 */
Number.prototype.format = function(format) {
  if (! isType(format, 'string')) {return '';} // sanity check
  var hasComma = -1 < format.indexOf(',');
  var psplit = format.split('.');
  var that = this;
  // compute precision
  if (1 < psplit.length) {
    // fix number precision
    that = that.toFixed(psplit[1].length);
  }
  // error: too many periods
  else if (2 < psplit.length) {
    throw('NumberFormatException: invalid format, formats should have no more than 1 period: ' + format);
  }
  // remove precision
  else {
    that = that.toFixed(0);
  }

  // get the string now that precision is correct
  var fnum = that.toString();

  // format has comma, then compute commas
  if (hasComma) {
    // remove precision for computation
    psplit = fnum.split('.');

    var cnum = psplit[0],
      parr = [],
      j = cnum.length,
      m = Math.floor(j / 3),
      n = cnum.length % 3 || 3; // n cannot be ZERO or causes infinite loop

    // break the number into chunks of 3 digits; first chunk may be less than 3
    for (var i = 0; i < j; i += n) {
      if (i != 0) {n = 3;}
      parr[parr.length] = cnum.substr(i, n);
      m -= 1;
    }

    // put chunks back together, separated by comma
    fnum = parr.join(',');

    // add the precision back in
    if (psplit[1]) {fnum += '.' + psplit[1];}
  }

  // replace the number portion of the format with fnum
  return format.replace(/[\d,?\.?]+/, fnum);
};