Curency Converter

Rates: if the combined total is > 50 then rates are 0.50 and 0.60 otherwise they are 0.58 and 0.60

Notes:
Coins:

JavaScript / ECMAScript used in this webpage.

function IsNumeric(sText) {
   var ValidChars = "0123456789.";
   var IsNumber=true;
   var Char;
   var Dots = 0;
   for (i = 0; i < sText.length && IsNumber == true; i++) { 
      Char = sText.charAt(i);
      if (Char == '.') { Dots ++; }
      if (ValidChars.indexOf(Char) == -1) {
         IsNumber = false;
      }
   }
   if (Dots > 1) {
      IsNumber = false;
   }
   if (sText == ".") {
      IsNumber = false;
   }
   return IsNumber;
}

function calculateEuros() {
   var sEurosNotes;
   var sEurosCoins;
   var flConvRate_Coins;
   var flConvRate_Notes;
   sEurosNotes = document.getElementById("number_of_euros_notes").value;
   sEurosCoins = document.getElementById("number_of_euros_coins").value;
   if (!IsNumeric(sEurosNotes)) {
      sEurosNotes = 0;
   }
   if (!IsNumeric(sEurosCoins)) {
      sEurosCoins = 0;
   }
   if (sEurosCoins > 0 || sEurosNotes > 0) {
      flConvRate_Coins = 0.58;
      flConvRate_Notes = 0.68;
      /* Combination Check
      if ((sEurosCoins + sEurosNotes) > 50) {
         flConvRate_Coins = 0.50;
         flConvRate_Notes = 0.60;
      }
      */
      if (sEurosCoins > 100) {
         flConvRate_Coins = 0.60;
      }
      var num = (sEurosCoins * flConvRate_Coins) + (sEurosNotes * flConvRate_Notes);
      document.getElementById("calculation_result").innerHTML = "£ " + num.toFixed(2);
      num = (sEurosCoins * 1) + (sEurosNotes * 1);
      document.getElementById("euro_input_value").innerHTML = "€ " + num.toFixed(2);
   } else {
      alert("Sorry, those do not look like valid numbers :-(");
   }
   return false;
}