What is the watch bezel slide rule?
A slide rule is a circular scale that either surrounds the watch face as a bezel or is located on the inner flange. It can be rotated in either direction, allowing you to perform various calculations related to time, speed, distance, and conversions. They are a valuable aid for performing quick calculations on the fly. Slide Rules were the pre-eminent calculating tool from their invention in around 1620, right through to their demise in the late 1980s, some 350 years later, but their decline really started in the 1960s with the advent of electronic calculators and computers, .The slide rule was universally used for nearly 400 years and was the most commonly used calculation tool in science and engineering until it was replaced by the pocket calculator.Slide rules are still commonly used in aviation, particularly for smaller planes. They are being replaced only by integrated, special purpose and expensive flight computers, and not general-purpose calculators.The slide rule was invented by William Oughtred in the 1600’s, but only began to be widely used in the mid 1800’s after a French artillery officer named Amedee Mannheim developed a version that became popular among engineers. By the early 1900’s engineering students in the US were commonly taught to use slide rules.OTIS KING, a London engineer, wrapped several feet of scales around a pocket-size cylinder in 1921 to achieve a portable slide rule with impressive resolution. FABER-CASTELL 2/83N slide rule is considered by some to be the finest and most beautiful slide rule ever made.
Why do GMT watches have rotating bezels?
The bezel was designed to rotate bidirectionally so the wearer can easily set any hour to conform to the GMT hands. This way, you can instantly track a second time zone with the bezel while the main dial continues to track the standard time. Rolex has two different types of 24-hour bezels: a stationary one as seen in the Rolex Explorer II, and a rotating one like the one used in the GMT-Master and GMT-Master II.