The thermal cycler (also known as a thermocycler, PCR machine or DNA amplifier) is a laboratory apparatus most commonly used to amplify segments of DNA via the polymerase chain reaction (PCR). The Polymerase Chain Reaction (PCR) is an important tool for many applications. For example, it can be used to amplify a sample of DNA when there isn't enough to analyze (e.g. a sample of DNA from a crime scene, archeological samples) as a method of identifying a gene of interest, or to test for the disease.