Interesting find here. looks like its a laser that gets mounted to the side handle of your chainsaw and helps aid with measuring the length of logs to cut.
www.firewoodprosizer.com
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Firewood ProSizer: A laser attachment for chainsaws to guide your cut | Firewood ProSizer
Laser measuring tool for your chainsaw. No need to paint, chalk or use your bar. Let the laser guide your cut for same size logs.