Fine tuning of Z height at zero

Printed first layer of the model has to smaller than equal to the first layer height in slicer.   After upgrading MK2S to MK2.5S, I did fine tuning of Z height at zero by measuring the thickness of first layer.

I set the first layer height to 0.3 mm for the calibration model.  After printing the first layer of the model, I stopped the printer, and measured the thickness of the sheet using a vernier caliper. The measurement was 0.4 mm.  The below image has tiny holes around edges and corners which indicates under extrusion. Does it?

I printed another sheet and added -0.1 mm to previous Z offset using Live Z function. The thickness of the second sheet was 0.35 mm to 0.30 mm.  Now the calibration is done.