its a virtual unit , you can make of it what you wish within the scope of decimal divisibility.
if you wish to alter a preexisting mm-unit drawing ..scale the whole drawing by a factor of .001 and thereafter assume your unit =1m..and carry on drawing per meter.

don't be so lazy. just hit that 8000. easy huh!

unedited, you appear to be scaling in the wrong direction. .dwg wants an existing line of 8000 to measure 800.

.dwg, the base unit is whatever you want. if you want 1 unit to be 1 cm, you draw 1 unit as 1 cm. to convert a drawing where 1 unit = 1 mm, scale it up by 10.

autocad appears to be designed to have 1 unit = 1 mm, and it's generally easier to work that way because what unit you choose in modelspace affects how you scale paper space viewports.

as you probably know, when drawing with 1 unit = 1 mm, to scale in paperspace to 1:100 (for example), you zoom 1/100xp.

however, with 1 unit = 1 cm in modelspace, you need to zoom 1/10xp in paperspace, because the base drawing in modelspace is 10 times the size.

this gets complicated with scales like 1:5, because you cant enter 1/.5xp as a zoom factor.

i don't work on autocad anymore, so can't confirm what i just wrote, but i'm pretty sure it's correct. i've drawn both with mm and cm, and the easiest option is to keep the same scale project wide so you don't have to mess around scaling drawings up and down when they come in from other consultants.

you may just get used to using the numeric keypad to enter all the numbers.

- oy yes,apologies...I read m. in place of cm...(so convert your mm-based drawing by 0.1 and thereafter assume 1 unit=1cm)


I personally prefer to draw in m. units (unless its an orphaned detail).
Then change to 1/1xp if wanting 1/100 scale in paperspace..

Any other scale is relative to the 1/00...20/1xp= a true 1/5xp.



With a (mentally assigned) unit of 1cm.. 1/.5 xp=2/1xp :) that, you can enter.(y scratch your left ear with your right hand..)

Whichever way/unit you consider to be the easiest, that ease is more a consequence of habit-familiarity than an inherent Autocad property (inter-unit format) . All other variables can be calibrated to reach the same end plot result.
Your drawing is an elastic piece on a flat balloon.

got it.
thanks. i figured out mark's method a while afterwards.
i haven't worked on autocad for a while so it took me some time to wrap my mind around scaling and such. and i forgot that modelspace was mm originally.. etc.
all the other scaling tips will be useful in the future, no doubt.