code: function _callDelta(s, k, t, v, r)
  {
    var w = bs.getW(s, k, t, v, r);
    var delta = null;
    if(!isFinite(w))
    {
      delta = (s > k) ? 1 : 0;
    }
    else
    {
      delta = bs.stdNormCDF(w);
    }
    return delta;
  }
docs: Calculates the delta of a call option.
  
  @private
  @param {Number} s Current price of the underlying
  @param {Number} k Strike price
  @param {Number} t Time to experiation in years
  @param {Number} v Volatility as a decimal
  @param {Number} r Anual risk-free interest rate as a decimal
  @returns {Number} The delta of the call option