Matt Sibum shares a useful option for the XLine command in AutoCAD.
"I have always used the XLine command to draw construction lines on drawings. Recently I discovered another option when entering the command: Bisect. To use this option, specify a vertex point, then the first angle, followed by the second angle, and AutoCAD draws an xline halfway between the two angles. In the past, I would draw an arc between two angles, followed by a line from vertex to midpoint of the arc, to get the exact same line that this function performs in a fraction of the time."
Notes from Cadalyst Tip Patrol: So many times we (by we, I mean me) use commands and tools in AutoCAD, but we forget that most commands have options as well. If we don't look at the Command line from time to time, we won't notice these options. The XLine command, which creates a construction line that extends infinitely in both directions, has several options. It is drawn by selecting two points. The other options available to us are to draw the xline horizontally, vertically, at an angle, at a bisected angle, and at an offset. Simply start the command, type in the appropriate option, and follow the onscreen instructions.