Precisely measure chain elongation to see if you need to replace your chain. These gauges give a more accurate reading than alternatives because they’re designed to anchor to a roller and extend across several links. A color indicator helps you quickly measure the space between rollers. If the gauge rests on top of the chain and you see green markings, your chain doesn't need to be replaced. If it slips between two rollers and you only see red markings, it’s time for a replacement.