A simple calibration plate (in inches) I use for testing what dimensions my printer will actually print at with given dimensions for profile and pocket shapes. Each feature is 0.5", 0.4", 0.3", 0.2" and 0.1". At some point I'll look at making a metric version.

Print it, grab some calipers, measure each profile feature and see how far it is off from the actual model. Then compensate accordingly with your part design work.

There are blank and 0.2mm layer (labeled) versions. FreeCAD source included.