Changing units midway through a drawing

Hi Guys,

I began drawing using "Inch" as "Main drawing unit" under "Units" in "Current Drawing Preferences". I'd now like to draw a few lines using "Millimeter". Even though I select "Millimeter" in "Current Drawing Preferences" LibreCad keeps using "Inch" to offset, draw etc.

How can I draw using Millimeter when I initially started off with Inch?

Thanks,

LibreCAD basically just thinks in units only, whether inches, mm, miles, parsec or whatever mainly just is a naming (has some effects on dimensioning style and other minor things). If you switch a drawing from inches to mm a line 10 inches long will then be 10 mm long. You will have to scale the drawing manually accordingly (x25.4). It doesn't happen automatically.
To switch back to inches it's x1/25.4. So it's not very practical to do this midway through a drawing.

Also see here: https://dokuwiki.librecad.org/doku.php/usage:howto#how_to_convert_from_mm_to_inches

Ive currently got measurements in Cm but i need them to be Mm , i have changed drawing preferences and applications preferences, but they still stay in Cm, am i missing anything or can you not change Units ?

It is also possible to change Length Factor in Dimensions tab of Current Drawing Preferences.
But this only changes dimensions, so it's good for printing.
But if the drawing is used for machine processing, I assume scaling is better.

Can't I specify the length in cm or mm like in Sketchup? In Sketchup, even if the base units are feet and inches, you can still specify the length in cm or mm if you need to.

You can specify the length in cm or mm, but sorry, no, you can't randomly switch the units for input during drawing. You only can convert the whole drawing to a different unit.
So best decide for certain units from the beginning.