This unusal tool is actually a Briggs and Stratton tool, but is recommended by Honda in a power equipment service bulletin. It's a vibratach, and is made in Germany. Inexpensive but wonderfully useful, the tech simply sets the tool to the rpm he wants the engine to run at, and then adjusts the engine's engine speed until the wire indicator wiggles in a figure-eight motion. Works best on single-cylinder engines, but I have used it on vertical twins as well. A useful tool.