JavaScript でのグローバルな名前空間汚染を回避するにはどうすればよいでしょうか?

var x1 = 5;
var x2 = 20;
var y1 = 3;
var y2 = 16;

var rise = y2 - y1;
var run = x2 - x1;

var slope = rise / run;

var risesquared = rise * rise;
var runsquared = run * run;

var distancesquared = risesquared + runsquared;

var distance = Math.sqrt(dinstancesquared);

var Calculate = function () {
  // Local variables
  var Coordinates = [];
  var Coordinate = function (xcoord, ycoord) {
    this.x = xcoord;
    this.y = ycoord;
  };

  return {
    // Exposed methods
    AddCoordinate: function (x, y) {
      Coordinates.push(new Coordinate(x, y));
    },

    Slope: function () {
      var c1 = Coordinates[0];
      var c2 = Coordinates[1];
      return (c2.y - c1.y) / (c2.x - c1.x);
    },

    Distance: function () {
      // Local calculations
      var c1 = Coordinates[0];
      var c2 = Coordinates[1];

      var rise = c2.y - c1.y;
      var run = c2.x - c1.x;

      var risesquared = rise * rise;
      var runsquared = run * run;

      var distancesquared = risesquared + runsquared;

      var distance = Math.sqrt(distancesquared);

      return distance;
    }
  };
};

// Self-executing closure
(function () {
  var calc = Calculate();
  calc.AddCoordinate(5, 20);
  calc.AddCoordinate(3, 16);
  console.log(calc.Slope());
  console.log(calc.Distance());
})();