The Place XY Dimension function places a special purpose line that is designed for dimensioning areas of drawing.
This function automatically activates the ortho mode while placing the line, however this can be released by pressing the <T> key.
Once the dimension line has been placed it can be grabbed and stretched from either end using the Grab Component function.
The dimension line can also be grabbed in its entirety from the middle.
The size of the arrowhead on each end, and the thickness of the line, is a function of the text size that is defined in the Sizes tab of the Setup Parameters dialog box.