The wear limit of modern O-ring chains is 0.6%. Chain manufacturers and professional workshops and race teams use digital measuring devices to decide if a chain is worn out or not. For private use there is an analog alternative. Seal ring chains (O-, X-, Z-, Quad-Ring) wear out faster due to extremely adhesive chain sprays. When you have to retighten your chain in the first 15.000 km, you need this device to document the damage caused by your "greasy" chain spray. Checking by "lifting" the chain as usual in the past with open roller chains is not suitable for sealing ring chains, because O-ring chains may only achieve 0.6% increase in length. With this tool this check can now be carried out quickly, precisely and very easily in the handling.