Working with scale in layouts.

When using the “zoom” command followed by (scale) 1:150 is achieved with a zoom scale of 66/10XP. How does this command work then? Why not enter 1/150XP?

First let us assume that you are using the command “mview” to creating windows in your presentation layout (or in paperspace depending on your version of AutoCAD). So, what units are you using?

Lets say you are metric and drawing in meters.
MODELSPACE: 1 unit = 1 m = 1000mm

And let us say that presentation is in millimetres (this is typically so for such layouts):
PRESENTATION/PAPERSPACE: 1unit = 1mm
So the drawing as seen through the window in the layout has to be scaled relative to that layout – hence we use the XP parameter.

CALCULATION
1:150 means that 1mm printed = 150mm modelspace
150mm in modelspace is 0.150units
This is a zoom of 1/0.15
For clarity let us enter the zoom value multiplied by 1000.
So switching to modelspace through the window in our layout (tilemode=1) we enter a zoom of 1000/150XP.

Remember: the two values in the zoom ratio have to be of the same unit (m:m, ft:ft). So your suggestion of 1:150 is correct only if drawing units are mm in modelspace OR the layout is in meters.

Your friend is right if the situation is the same as described above (drawing in m, paper in mm) but it seems a perverse form of saying the same thing and is not as accurate. (1000/150 is 6.6667, 66/10 is 6.6)

Above all it is much simpler to remember that when drawing in m and printing in mm you only have to enter the zoom as:
1000/(desired-scale)XP

Originally posted on Yahoo! Answers