Polar tracking is a precision feature available in AutoCAD. Polar tracking allows you to snap onto a preset angle and move a specified distance into the respective direction.
Below I use polar tracking for creating a line in AutoCAD.
I enter the LINE command. I then click on the starting point where I want the line to begin.
The currently preset angle is 90 degree. I can change the angle, as show in the figure below, by moving the cursor. I can then enter the distance which the line should measure into that direction. I press enter and the line is complete.