some erratic operation causes
Watch not cleaned and oiled properly.
Bent wheels or bad tooth on wheel or pinion.
Hands hitting on face, together, or on crystal.
Stem not staying in.
Watch is magnetized.
Rust, oil, or dirt on hairspring.
Out of beat.
Balance pivots loose in jewels or damaged balance jewel.
Broken or dirty jewels.
Loose roller jewel.
Mainspring sticking or binding in barrel.
Excessive wear in barrel causing it to rub on plate or bridge.
Motion work not free.