This command simply changes the size of the object you created or from the existing object created by someone else. So to start, let us make an object, on this example, two rectangles that overlaps each other. To change the size or scale, first type “scale” on the command prompt and press enter. AutoCAD will prompt you to select an object. Select the two objects either by selecting the two with the selection box or windowing to select both. To window it, just type “w” on the command prompt and press enter. The AutoCAD will prompt: Specify first corner: pick the first point in windowing the object on the lower left corner of the two rectangles (see Fig. 1). Then drag the window to enclose the object and click the upper right corner outside the object then press enter.
Fig. 1 – Windowing an Object to Select
Then AutoCAD will prompt: Specify base point: which tells you to specify a base point. A base point is point in the drawing area for relative distance and angle when scaling, copying, moving, and rotating objects. To make it simple, when you pick a rubber band, when you hold it first with your right finger, thats the base point. As you stretch it with your left finger, your right finger holds the other end in a steady and fixed position. So your right finger that hold the rubber band is the base point.
So specify a base point by clicking your mouse near or center of the two rectangles. Then you will see another prompt: Specify scale factor or [Reference]: you will notice that as you move your mouse and drag your cursor, the two rectangles changes its size. From that point you can just click your cursor to change the size but if you like a more accurate dimension, you can specify the scale factor. If you wll type “2” the size will be twice as big as the original. If you type “3” the size will be three times. If you want to use the “Reference” option, it is use for copying the size of another existing object.
To make an example, make another rectangle on the side of the two rectangles you’ve already drawn. Make the size of the third rectangle half the size. Then run the command again by typing “scale” and select only the two rectangles you have drawn excluding the third rectangle then press enter. Specify the base point by using osnap command on the right lower corner of the rectangle ( See Fig. 2 ). Set the osnap command first to “endpoint”. Press “shift” + right mouse button and select osnap setting. Check the “Object Snap on” box and Object Snap Mode > “Endpoint” box and click OK. After specifying the base point, AutoCAD will prompt : Specify scale factor or [Reference]: then type “r” to invoke the subcommand “reference”. Then another prompt will show: Specify reference length <1>: and click the base point again then on the Specify second point: click the upper corner as in Fig. 2. Then another prompt Specify new length: will appear. This is a bit tricky because you have to use osnap command again. While holding the shift key click the right mouse button and when the osnap menu appears select Point Filters > “y” then select the upper left corner of the reference rectangle ( See Fig 3). When the prompt Specify new length: .Y of (need XZ): appears, select the base point again. Now you will see that the height of the rectangle duplicates the reference rectangle.
Fig. 2 – Using the Reference Command to Specify Base Point
Fig. 3 – Using Osnap Filter to Specify New length