#3 Line of Fire Tool
Figuring out line of fire (LOF) is critical during games. It needs to be quick, fast, and reliable. So forget that chart in the back of the rulebook!  The easiest and most common method is to use a line of fire tool. The tool can be as simple as a piece of string or as complex as a laser pointer.

Probably the most common tool used is the ID badge clip. These can be found at any office supply store and have a retractable string attached to them. Place one end in the target square and pull out the string until you get to the originating square. When your done it rolls itself back into the badge clip for easy storage.  It's exact, cheap, compact, and easily replaceable if lost.

The perfect solution!