Bed height map - Wrong result data

I have calibrated carriages on all three towers with rod as in your video tutorial, and double checked geometry of the printer with laser measuring device (0.1 mm resolution) and metal meter and everything is OK.

Printing with 0.1 mm layer height is excellent and even on the whole bed.

But, when I try to measure levels with micro-switch probe mounted on the print head, with Bed height map option in the Repetier Host, I got wrong results. Only center point is correct. Why is that? What I am doing wrong, because printing is OK end even on the whole bed?

I got results Min Height: 11.82, Max Height 15.33, Center Height 14.11. Maybe I can make level mistake of 0.1 mm, but more then 3 mm no way.

Please advice.

Thanks in advance.

Dragan Kujovic