Ways to compute distance between two points

Discussion created by orsela1@gmail.com on Feb 21, 2011
Latest reply on Jul 16, 2013 by AxtriaInc
I Tried computing the distance between two points using several different ways, and in some I got different results. I wonder what could be the reason.

First, I created a polyline and added the two points to it and used IPolyline.Length property.
After that I used IProximityOperator.ReturnDistance. I got the same result using these methods.

Then I tried using IMap.ComputeDistance and got a different result.

I got even more confused when I tried drawing the points on the map and measuring the distance between the points using the MapMeasureTool. When I measured the distance using Meters as the unit, I got the result of the first two methods (converted to Meters, of course). When I changed the tool units to Decimal Degrees (my map units), I got the result of the third method (IMap.ComputeDistance).

Am I missing something basic here?