The Cyclo Chain Wear Indicator helps you determine when your bicycle chain needs replacement due to wear. It measures both 0.75% and 1% elongation. To use, orient the tool for the desired measurement. Lower it onto the chain, engaging the bridged end over a roller. Allow the spiked end to drop; its resting position indicates chain elongation. Position 'A' signifies good condition. If the tool rests at position 'B', the chain has exceeded the manufacturer's specified elongation and should be replaced. A position between 'A' and 'B' indicates the severity of the chain's wear. Replace a worn chain to prevent damage to other bicycle components. This tool is made from high-quality materials and engineered for durability.