If you set up a paper space drawing (D Size, whatever) and set the paper space scale to 1:100, 1:200, whatever...and the drawing in model space was drawn in real world units, then it should plot at the paper space scale specified.
Plotting to scale from model space takes a little trial and error. First draw a rectangle the size of your paper minus the margins required. For scale of 1:100 use the SCALE command to scale the rectangle 100 times. Put this rectangle around what you want to plot then plot using Window and select the corners of the rectangle. Use scale to fit for the scaling and print it out. Measure the print with a scale and you may need to adjust the size of rectangle and try again.
Thank you. I'd still like to understand how to set the plot at scale directly from model space as it seems simpler. I'm new to plotting, as you can easily tell... that's why I'm a bit confused...The drawing is drawn in mm at true scale and I have to plot it at scale 1:100. So when I open the plot window I set the paper size and the scale to mm. In the scale box I'm not sure if I did it right: there are mm and units. I tried to put 1 mm to 100 units...I plotted it and it comes out ok I think...I'm not sure what units are. If this prints correctly, I'm guessing units refer to mm in model space and mm to mm on the printed sheet. But if that is so, then how can 100 units = 1 mm in the plot window how I just set it; if the drawing in model space is already in mm, then 100 units should be 100mm. I'm confused.
I resisted paperspace for a long time. Once I dove into it (help explains it well), it does make things easier.
But when I plotted from model space to a scale in the old days (and note: the previous process given you sounds good to me), I would determine the actual drawing plot area (i.e. if plotted D Size 24"x36", then I'd assume I'm going to get a plot area of 22"x34"). Then I draw a box around my model space objects with that aspect ratio. I size the box using the math of the desired plot scale (i.e. if I want 1:200 and my drawing is in mm, the bounding box should be 111,760x172,720 which is 22x34 x 25.4 mm/inch. x 200) The box also lets me see if, at that plot scale, my drawing fits reasonably at that scale and by moving the box around, you can arrange the objects in the box ( onplotted paper). Then if you plot "extents and set the scale, rob's your mother's brother. Once you are happy with everything, you can put the box extents bounding box on a layer that is set not to plot, so it doesn't show up.
As said before, the plot scale area in the dialog box is clear (you just need to get your mind arund it via experience). The Scale settings set the ratio of model space units on the left to plotted units on the right. The "Units" is tied to the entry above it and reflects the scale choosen above that. If you set a scale of 1:200 and you set the desired plot unites to mm below that, then 1 mm will plot as 200 mm and the units says "200" because that is the scale you set. If you say "Custom" in the scale, then set 1 & mm below that, then 200 below that at "Units", that would be exactly the same as plotting 1:200 for a specified scale.
As a QC, create a drawing only with a box at an even size, plot it, then measure it on the paper factoring in the scale to see if you got it right.
All this being said, nowadays, this is overly laborious. Paperspace simplifies the heck out of all of this. I'd advise you to get hip to it.
I digress. I learned paper space via Lynda.com. Get a one month subscription (or a year and learn lots), then watch Bartletts training videos. I went from knowing nothing about paperspace to plotting like a pro before the day was over.