I saw an episode of Ask This Old House about a month or two ago. During the show, when they preview new and different tools, they featured a tool that receives a can of spray paint and has a wheel with a dial that would allow you to adjust length. In the end, what happened is you roll the wheel down a log that you wanted to saw for fire wood and depending on where you had the distance dial set it would shoot a dot of spray paint every 16", for example, so you would know exactly where to cut the log to get the perfect sized wood for your fireplace.
I would love to have one of these, but I've been unable to find one. Any help you could give me to assist in finding this would be greatly appreciated!!!