With Autodesk® AutoCAD® Polar tracking while drawing a line for example, the Relative to last segment the Relative Polar angle will be 180 degrees.
Hence if you want to draw a line with an angle of 45 degree from that line you would have to add 180 to 45 or subtract 45 from 180.
With this command, RLP sets the Relative Polar angle to 0 (Zero). One of the options in this app is Direction.
If the angle is going clockwise you hit Direction on the command line or type in D and hit enter and it changes the angle direction to the opposite of what the current one is.