When trying to document a layout with exact geometry one quickly notices that a lot of layouts one builds with real track do not work using a CAD system or some track layout program. This is due to the so called "vario system" which allows some play when joining the tracks, so that with some wiggling around one can make layouts line up perfectly with no danger of derailing the trains, that don't use the exact geometry of the pieces. This is achieved by making the pegs somewhat smaller than the holes. The round part of the hole sometimes is not even being part of an exact circle, but rather an ellipse allowing the tracks to connect with a small gap between them. Also the neck doesn't have a sharp edge at the end of the track but is carved round. This may have started as a production loss or to make it easier for small children to join the tracks. Some sources state that Eichhorn was the first to design the connections thususing systematicallythis system.
