Make exact dimension of 609.6mm

I set up a sheet with a scale factor of 3.5 and want to create a dimension exactly 609.6.
However, the Modify → Lengthen tool does not allow me to select the dimension object.

Hello!

I would delete the dimension, and then make a new according the new lenght.

How can I make a new dimension without making its length with the mouse?

Have pressed Dimension-Vertical and get

Specify first extension line origin
Specify second extension line origin
Specify dimension line location

Enable line end snap from the bottom.

Don't know how to do without a mouse.

That has been discussed here before, you can't use LibreCAD or any other efficiently without a mouse.

Welcome Heime!

Just get used to the command line and relative coordinate input, that's what you need.

See:
https://docs.librecad.org/en/2.2.0_a/guides/cmdline.html
https://docs.librecad.org/en/2.2.0_a/ref/fundamentals.html#relative

Armin

yes, lengthen operates with lines, not with dimensions. Of course, it is possible to move dimension points by mouse, yet it will be hard to find precise distance (at least, until 2.2.2 where informational cursor displays relative coordinate (distance, angle from relative zero).

So the logic is something like this:

1) make sure that you have 2 points located in desired distance. If necessary, you can create temporary line with needed lenght.
2) remove existing dimension
3) create new one using these two points - for line, for example, you may use snap to endpoints.
4) if line is temporary - delete the line.