Editing Gyroscope (section)

===Ring laser gyroscope===
{{Main article|Ring laser gyroscope}}
A [[ring laser gyroscope]] relies on the [[Sagnac effect]] to measure rotation by measuring the shifting interference pattern of a beam split into two separate beams which travel around the ring in opposite directions.

When the [[Boeing 757]]-200 entered service in 1983, it was equipped with the first suitable ring laser gyroscope. This gyroscope took many years to develop, and the experimental models went through many changes before it was deemed ready for production by the engineers and managers of [[Honeywell]] and [[Boeing]]. It was an outcome of the competition with mechanical gyroscopes, which kept improving. The reason Honeywell, of all companies, chose to develop the laser gyro was that they were the only one that didn't have a successful line of mechanical gyroscopes, so they wouldn't be competing against themselves. The first problem they had to solve was that with laser gyros rotations below a certain minimum could not be detected at all, due to a problem called "lock-in", whereby the two beams act like coupled oscillators and pull each other's frequencies toward convergence and therefore zero output. The solution was to shake the gyro rapidly so that it never settled into lock-in. Paradoxically, too regular of a dithering motion produced an accumulation of short periods of lock-in when the device was at rest at the extremities of its shaking motion. This was cured by applying a random [[white noise]] to the vibration. The material of the block was also changed from quartz to a new glass ceramic [[Cer-Vit]], made by [[Owens Corning]], because of helium leaks.<ref>Donald MacKenzie, ''Knowing Machines: Essays in Technical Change'', MIT Press, 1996, Chapter 4: ''From the Luminiferous Ether to the Boeing 757''</ref>