If you are interested in one, I put the graphics for it in these two threads:
http://www.subsim.com/radioroom/showthread.php?t=140397
http://www.subsim.com/radioroom/showthread.php?t=140421
You print them out, then cut them out and pin them together, and you'll probably want something to use as a cursor.
If you aren't familiar with the techniques of making "wheels", see these threads:
http://www.subsim.com/radioroom/showthread.php?t=106923
http://www.subsim.com/radioroom/showthread.php?t=114351