The voltage-controlled oscillator in most phase-locked loops is built from a ring oscillator.[5] Jitter of ring oscillators is commonly used in hardware random number generators.[3][4][6] A ring oscillator is often used to demonstrate a new hardware technology, analogous to the way a hello world program is often used to demonstrate a new software technology.[7][8] Many wafers include a ring oscillator as part of the scribe line test structures. They are used during wafer testing to measure the effects of manufacturing process variations.[9] Ring oscillators can also be used to measure the effects of voltage and temperature on a chip.[10]