QGIS lock mapscale for project

I try to create a QGIS project with a fix scale of 1:50.000. I set the scale in the status bar on the value and save the project. But if I open the project on another PC the scale 1:48699.
I tried the lock function, but it has the same results.

Is there another parameter which I can use?
I use the QGIS Version 3.4.8 LTR