Offset tool doesn't work properly

Dear community, I’m having trouble with the offset tool every now and then. Most of the times everything works just fine, I use the tool on an edge, type in a value of 6 cm and it sets it off by 6 cm. But: sometimes I type in a value of 6 cm and it sets it of by ∼5,48 cm. Same thing when I draw a guide line and drag the offset to it. Does that sound familiar to anyone? Can anyone help me with that please? Thanks and have a great day everyone!

Share an example .skp file where you are seeing this.

When that happens to me, I have found I moved the mouse accidentally by accident prior to committing the action.