Spin testing is an important step in the ensuring safety and integrity of high speed rotors. Rotating components used in modern, high-speed machinery operate under large centrifugal stresses and can fail with explosive force; so all developers and manufacturers of turbo machinery components need to test rotors for centrifugal strength. Developers need to calibrate and verify the results of stress analysis, and to establish the fatigue life of high-performance rotors; and manufacturers need to prove the strength of high speed disks before shipment and installation. The vertical axis spin test that fills these various needs was originally developed to solve a problem with military aircraft turbochargers during World War II, and has been in wide use ever since. While there are other ways to test for centrifugal strength, the vertical axis, flexible shaft spin test is most commonly used because it is the most versatile and general method available to spin a high speed rotor without requiring a high cost, elaborate bearing system for each rotor.