Posted by dellus on Feb 13, 2023; 11:25pm
URL: https://forum.librecad.org/How-to-Change-Scale-in-a-Designed-Architecture-Floor-Draw-tp5722488p5722495.html

It took me a while to understand what you mean with drawing scale (vs printing scale). So you want to use the screen grid to determine lengths. Out of the box the grid scaling varies dynamically to zoom ratio.
If you want a fixed grid size you have to set it at Options - Current Drawing Preferences - Grid. Assuming you have set units as Centimeter X-Spacing and Y-Spacing then have to be 20.
Using the grid to determine lengths is recommendable for occasional amateurs only. Professionals use input at the command line. More to learn.
I was not amused by the unfriendly words in your other posting, especially the last one.
We can be glad to have a manual like that at all, long time we didn't. If you had studied it properly you would have seen it tells about the grid settings and the Draft mode.