code: function getRho(s, k, t, v, r, callPut, scale)
  {
    scale = scale || 100;
    if(callPut === "call")
    {
      return _callRho(s, k, t, v, r) / scale;
    }
    else // put
    {
      return _putRho(s, k, t, v, r) / scale;
    }
  }
docs: Calculates the rho of an option.
  
  @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
  @param {String} callPut The type of option - "call" or "put"
  @param {String} [scale=100] The value to scale rho by (100=100BPS=1%, 10000=1BPS=.01%)
  @returns {Number} The rho of the option