As the founder of Rolex explained in 1927: “We all know that the pivots must run in oil, and oil attracts all those fine particles of dust, which constantly, although in only very small quantities, penetrate into all watch movements, however well the cases are made.

The rotary action of the pivots gradually makes a paste of the oil that thickens more as time goes on, and dust gets attracted and is mixed up with it.

This paste acts like emery paper on the very fine pivots and pinions and gradually they get worn away, very little of course, but sufficiently to cause bad timekeeping. […] Our Oyster excludes all dust and consequently it will always maintain perfect time.”