“My watch has stopped - Why?”
This is an excellent article from 1941.
  It provides you with a detailed look at why your watch may have stopped.

The purpose of these pages is to help the watchmaker explain to the owner of a watch, which is not running satisfactorily, what has gone wrong.  Few watch owners fully understand the intricate, delicate construction of a watch movement. The following illustrations of those flaws usually found when a watch is brought in to be fixed should simplify the task of explaining what repairs are needed.

When a watch has been jarred or dropped, the Balance Staff and Balance Jewel are likely to have been damaged.  Illustration No. 2 shows a perfect Balance Staff.  A Balance Staff which has been running in a cracked Jewel is shown in illustration No. 3. No. 3 and No. 4 depict bent and broken Balance Staffs.  Number 6 depicts a perfect Balance Jewel No. 7 and No. 8 show a damaged Balance Jewel might look like .  Defective Balance Staffs cause a watch to run too rapidly or too slowly.

No. 15 and No. 15A show a perfect Escape Wheel and one with damaged teeth. All fifteen teeth must be exactly alike for a watch to run correctly. No. 15B and 15C show a perfect Escape Wheel Pinion and one which has broken, thus stopping the watch.

The Minute Hand is attached to the Cannon Pinion, No. 19, which is fitted onto the Center Post.  This part may rust, or its may break.

No. 20 and No. 20A show set and unset Center Jewels which have been cracked by a bump, usually one which also breaks the crystal.

The Click, No.21, prevents the Mainspring from completely releasing and leaving the watch without power. Under constant pressure it gradually wears away and must be replaced.  The Click Spring, No. 22, which holds the Click, is very sensitive to atmospheric changes and breaks very easily.

When a Mainspring breaks, it may do so with sufficient force to break the Barrel, No. 24, the housing for the Mainspring.  The teeth may be jammed by the impact of the recoil, or the hooks which hold the ends of the Mainspring may give.  One of these hooks is on the Barrel Arbor, No. 24A.  An Arbor with a worn hook, stripped thread or defective square must be replaced.

The pin indicated on the Detent or Setting Lever, No. 30, wears off through the constant pull it exerts, causing possible loss of the Stem and Crown. The Setting Bridge, No.31, holds both the Detent and Minute Wheel in place. It is shown with a spring broken because of constant pulling of the Stem.

The Regulator, No.33, controls the rate of the Hairspring, causing the watch to run faster or slower as desired.  Should the pins which hold it become damaged, they must be repaired. 

A defective Clutch Lever, No. 32, caused the winding mechanism to lose control of the setting and winding of a watch.

A broken Mainspring, No. 36, one with a damaged outer end, No.37, or inner end, No. 38, will cause a watch to stop at once.  A new Mainspring must be installed

~~~  The End ~~~