By entering an expression in the command line calculator, you can quickly solve a mathematical problem or locate points in your drawing.
CAL command runs the 3D calculator utility to evaluate vector expressions (combining points, vectors, and numbers) and real and integer expressions. The calculator performs standard mathematical functions. It also contains a set of specialized functions for calculations involving points, vectors, and AutoCAD geometry. With the CAL command, you can
TheCAL evaluates expressions according to standard mathematical rules of precedence.
Mathematical operators in order of precedence 


Operator 
Operation 
( ) 
Groups expressions 
^ 
Indicates numeric exponent 
*, / 
Multiplies and divides numbers 
+,  
Adds and subtracts numbers 
You can use CAL whenever you need to calculate a point or a number within a command.
For example, you enter (mid+cen)/2 to specify a point halfway between the midpoint of a line and the center of a circle.
The following example uses CAL as a construction tool. It locates a center point for a new circle, and then calculates one fifth of the radius of an existing circle.
Here is the command prompr sequence:
Command: circle
Specify center point for circle or [3P/2P/Ttr (tan tan radius)]: 'cal
>> Expression: (mid+cen)/2
>> Select entity for MID snap: Select the notch line (1)
>> Select entity for CEN snap: Select the large circle (2)
Diameter/<Radius>: 'cal
>> Expression: 1/5*rad
>> Select circle, arc or polyline segment for RAD function: Select the large circle (3)
Calculate Mathematical Expressions in a Dialog Box
You can also enter and evaluate mathematical expressions in a dialog box using the following format: =expression<END>.