For modern watch movement, there is a "Fast , Slow"
- for easy viewing the parts which are similar to the
mechanical watch movement
The Balance Spring pass through a slot which is the
""Fast , Slow" handle"
|After removing the balance spring,
you can clearly see the slot (red ellipse).
If there is a "Fast , Slow" handle, we do not have
to remove the pin in order to adjust the Effective Length
of the balance spring.
Assume all factors are unchanged, if the Effective Length
of the balance spring is extended, the watch runs slower.
If the Effective Length of the balance spring is shortened,
the watch runs faster.
Balance Spring Effective Length = A to B
In page 1, the Unadjusted Movement does not have the
"Fast , Slow" handle; therefore, B is the
same as C which is the place of the Pin. So, removing
the pin is required for adjusting the accuracy of the
watch. Pull out the pin is easy; however, put it back
is nightmare !
On a modern watch movement, you can find the "Fast
, Slow" handle next to the end of the balance spring
C which is locked in place with a screw rather than
If you have to adjust the accuracy of a watch, you
can easily turn the handle to the left or the right
according to the indications : + faster , - slower.