coordinate system - Calculating distance between two points with esri.geometry in ArcGIS API for JavaScript?

The function getLength(point1, point2) should calculate distances between two points.

When I am trying to calculate distance between points having 100 meters between them

p1=new esri.geometry.Point(3997030.6690969253, 7444299.320646087, new esri.SpatialReference({ wkid: 102113 }));
Object
p2=new esri.geometry.Point(3996951.455397143, 7444142.154020177, new esri.SpatialReference({ wkid: 102113 }));
Object
esri.geometry.getLength(p1, p2)
176.00045037719127

I am getting 176 which is wrong. Projection is Web Mercator (WKID 102113).

---

@Krystian found that getLength uses just Pythagoras theorem to calculate length. So it gives length in projection meters. How to obtain distance in real meters?

Answer

Web Mercator Auxiliary Sphere is WKID 102100

http://resources.arcgis.com/en/help/arcgisonline-content/index.html#//011q00000002000000

var polyline = {
    "paths":[[[3997030.6690969253, 7444299.320646087], [3996951.455397143, 7444142.154020177]]],
    "spatialReference":{"wkid":102100}
};
console.log(JSON.stringify(polyline));
polyline = new esri.geometry.Polyline(polyline);
console.log(JSON.stringify(polyline));

polyline = esri.geometry.webMercatorToGeographic(polyline);
console.log(JSON.stringify(polyline));
console.log(esri.geometry.geodesicLengths([polyline], esri.Units.METERS));
//output 99.93917832865446

6.1 cm short, good enough for govment work?