IFC wall opening size missmatch

Hi,

IFC-file from Revit.

Door opening is 1010mm.


Measure opening in IFC-viewer (Solibri or BimVision): 1.010000m = 1010.000mm -> correct.

Opening (or ref) the same IFC-file in OBD.
Measure the same opening: 1012mm. 2mm wider.

...in Bentley View: 1010.02mm. 0.02mm wider.

Any ideas why?