Hi,
V5
measure 20 times and each time a different dimension !
what method is best to find the average of such or the middle value of one of those mountain range shapes, median ?
I know one might add them all up and divide by the number, but I would prefer the value for the most ‘together’ ones, the ‘median’
Is there a command to select the dims that all start at the end of my object and shows me a dimension from there that is the median ?

This is a typical reverse engineering application and while Rhino does have some tools that are reverse engineering oriented, its is NOT a dedicated reverse engineering tool. For a Rhino compatible plugin you should consider Mesh2Surface. The industry standard however is DesignX, which is roughly 10x the cost of Mesh2Surface.

My feeling is that you would manually need to obtain the median value, perhaps by computing the median from the multiple measurements, or from generating an interpolated model (ie quadRemesh with interpolated SubD option).