Point "a" and "b" of Timexes KEY SLOT replaced the regulator pins found in many watches. When setting up a hairspring in a traditional watch, the hairspring is closely centered between the brass regulator pins without touching them. If the hairspring moves by gravity from point "a" (inside)to "b" (outside) then it will cause the watch to loose or gain time as the ACTIVE LENGTH of the hairspring has changed in the hairspring's motion from point "a" to "b" or "b" to "a".
Timex built a triangular shaped arm (see above picture for a better view)into their regulator. The taper of this ARM enabled it to be bent to PUSH and HOLD the hairspring against the inside wall of the key slot "a", keeping the hairspring from moving by gravity to "b" of the key slot which would alter the active length of the hairspring.
Balance wheels have to be poised. Any uneven weight around the outside of the balance rim will cause the watch to gain or lose time in the various positions of the watch. Notice how the balance rim "a2" is narrow while the rim at "a1" is wider. The balance rim had to be wider at "a1" to counter-balance the weight of the coil at "a2". The circular drilled cavities in the balance rim were done at the factory to further adjust the watch for better positional timekeeping.
"D" is a non-movable stud. Many hairsprings have a movable stud to adjust the height of the hairspring.
Metal Contact Pin & D Shaped Insulative Jewel
"A" is the v-shaped balance pivot. The impusle pin "b" drives the lever (more about this later). "C" is the impulse table. "D" is the red "d" shaped insulative jewel. "E" is the metal contact pin. This pin makes contact with the end of the contact spring "d"(below). It is joined directly to the coil by a thin piece of coil wire. Note how this contact pin and wire are insulated from touching the balance, so they do not create a short.
"A" is the terminal spring (conductor). The negative part of the cell (battery) touches this spring. The negative portion of the cell must not touch any other part of the watch or it will cause a short. The spring is insulated from the main plate by "b." "B" is positioned between the frame and train bridge. It functions as a pillar to space them apart. The two dowels or pins locate the contact assembly in the plate without the need for a costly bridge or screws. "C" is a L-shaped arm that may be adjusted to change where "d" makes contact with the metal contact pin "e" (above). When "d" touches "e" the switch is closed and the coil is energized. The polarity of this electromagnet kicks the balance wheel around until it is drawn back by the hairspring. Contact is made two times in one oscillation of the balance assembly.
INSIDE Timex Electric BACKSET
Notice the two red colored jewels and the half-moon shaped wear to the contact pin in front of the lower jewel. It looks like someone took a bite out of a sandwich. This is where the contact spring/wire touches the contact pin. Pulling out the stem to the setting position when not wearing the watch will prevent unnecessary wear to the contact pin.