On June 26th, 2018, Lumetrics was awarded a new patent for “Associated Interferometers Using Multi-Fiber Delay Lines.” An interferometer apparatus which include two or more coupled fiber optic Michelson interferometers using fiber optic stretches which stretch two or more optical fibers wound around the perimeter of the optical fiber stretchers by the same amount is disclosed. Preferably a pair of reference and sample fiber optic stretches are utilized which run in a push-pull mode of operation. When one of the interferometers is a coherent light interferometer it can be used as a reference distance scale for all of the remaining low coherence light interferometer. A method for measuring a physical property of a device under test is also disclosed using the apparatus of the present invention. This patent allows the user to measure optical thickness at multiple locations on a sample or in a manufacturing line simultaneously with a single measuring instrument without the need of an optical switch. This enables faster measurement and continuous measurement capability 100% of the time.