Angelina Roskam, a CAD technician, describes different methods for using AutoCAD's Scale command.
"I often encounter drawings from others that are not drawn to scale, and the same can happen when you insert a PDF or other reference into a drawing. The Scale command is a simple way to save time and convert the drawing or reference to the correct scale so it is workable and accurate.
"You'll notice that when you enter the command and have picked your base point, you have two options: make a copy or scale it by reference. If you are making a copy, you can choose to copy what you want to scale to a new size. (Scale depends on your pick points and input values.)
"I find it handier, however, to scale by reference after entering the command. If you know the length, width, height, etc. of a line or object on a drawing and it is not to scale, simply enter the command, select the base point, execute 'reference' (or 'R') in the command, then re-select the base point, the second point, followed by the reference point or value you'd prefer it to scale at. This saves a lot of time trying to re-draw any drawings that are not drawn to scale, and it's also very useful when inserting a PDF or image at the correct size."
Notes from Cadalyst Tip Reviewer Brian Benton: The reference option in scaling can be a bit tricky, especially if you haven't used it very much. Typically users will scale by reference (1, 2, 3, etc.); the size of the object doesn't matter.
Scaling by factor changes the size, no matter what it is, by a factor. For example, a factor of 2 doubles the size. A factor of 0.5 will reduce the object by half.
Scaling by reference, on the other hand, will change your object from one specific size to another specific size. If you had a square that was 5 units on a side and you want it to be 10 units on a side, you have two choices: Scale it by a factor of 2 or by a reference of 5 to 10. This is easy enough to scale by a factor of 2. Say you wanted the square to be 3.14 units. What is your scale factor? You could take the time to do the work, or you could let AutoCAD do it for you. Use the reference option. Enter a base length value of 5, because that is the actual length of the square's side. Then enter the length you want it to be, regardless of scale factor. This is very useful when you want something to change to a specific length.