Units: one of the most commonly used commands

Units command is used to control the precision and display formats for coordinates, distances, and angles. The shortcut key is UN.

After executing the UNITS command, the following dialog box will pop up, shown as below,

Units settings mainly include the following functions:

1.Set the display formats for coordinates,length, lighting and angles

For length, users can set it to Decimal, Fractional, Engineering, Architectural and Scientific; for angle, users can not only set it to Decimal Degrees, Deg/Min/Sec, etc, but also set it clockwise. The display formats can be adjusted according to users’ needs.

2. Set the precision for value and angle, which determines whether to display numbers with decimal points and the number of decimal places

Here it controls the precision for angle display in Properties Panel, command line and dialog box, which affects how we perceive precision instead of the actual CAD drawing precision, for instance, the Z-coordinate seems to be 0 but when you get “non-coplanar” prompt when using fillet; the scale of both blocks are 1 but look different, all of them is the result of setting precision without decimal places.

3. Set units to scale inserted content

The units here are the familiar ones such as meter, centimeter, millimeter, inches, feet, etc. Many would think this unit as the actual drawing unit, for example, users might think when the unit is set to meter, and when we a unit of line segment and the length would be 1 meter, and when we change the unit to millimeter, and a unit of the length would be millimeter, however, this is not the case. Actually, set the unit is to meter, and draw a line of 100 units, then change the unit to millimeter, measure this line again, the line is still 100 units, or we can create a new drawing and set the unit to inches, then copy this 100-unit line to this newly-created drawing, this line measures at 100 units, which is why we call the units here Insertion scale.

Insertion scale controls the unit of measurement for blocks and drawings that are inserted into the current drawing.

There are two main ways to insertion: one is to insert drawings to other drawings as a block; another is to insert drawings to other drawings as xref.

When inserting drawings to another drawing as a block or xref, the CAD system will changing the scale according to the two drawings, let’s say there is a drawing with units set to millimeter and when it is inserted to another drawing with units set to meter, the drawing will scale down 1000 times to make sure the two drawings match in size.