EBAUCHE
Incomplete (jeweled or non-jeweled) watch movement without  regulating organs, mainspring, dial and hands.

ENDSTONE
Undrilled jewel, placed on the balance-staff pivot resting against its flat surface, to reduce pivot friction. Sometimes used also for pallet staffs and escape wheels.

ENGINE-TURNED
Guilloche.

EQUATION OF TIME

The mean time that we use to keep track of the passing of the day 924 hours evenly divided into minutes and not seconds) is not equal to true solar time. The equation of time is a complication devised to show the difference between the mean time shown on one's wristwatch and the time the sun dictates.

EQUINOX
The time when day and night are of equal length, when the sun is on the plane of the equator. Such times occur twice in a year : the vernal equinox on March 21st-22nd and the autumnal equinox on September 22nd-23rd.

ESCAPE WHEEL

A wheel belonging to the mechanism called escapement.

ESCAPEMENT
The part of a watch movement which controls the speed with which energy escapes from the main spring. The combination of the balance, balance spring, pallets, and escape wheel, a subgroup which divides the impulses coming from the spring barrel into small, accurately portioned doses. It guarantees that the gear train runs smoothly and efficiently.