Hi,
a short attempt to explain what you see in the video, here's Alec's pic again with some additional darwing:
The yellow arrow indicates the fourth wheel, it's the last regular gear wheel
of a classical going train and usually turns
one time in a minute - thus
naturally showing seconds. You may recognize the position in this movement would
place the small seconds precisely at 6 o'clock position. As can be seen by
the arrow, it turns CCW, which means seen from dial side
it's cw as it should
be :-)
The blue arrow indicates the wheel of the jumping center second - as indicated and viewed from the bridge side CCW as well, CW viewed from dial side.
The red arrows - those are indicating the tiny pinnion which connects the
fourth wheel to the center seconds wheel - but
due to the special "floating"
design it translates the regular (5 increments/sec. as caused by the
escapement) movement
of the fourth wheel into a "jumping second" at the
center seconds wheel.
Floating, that means the post in the center of the pinnion is fixed in a
way allowing for lateral movement.
This is done by means of an adjustable
spring which is also responsible for the advancement of the center
seconds.
It's quite easy to observe in the video, how the transmitting
pinnion slides sideways to the left (one red arrow)and reaching a certain
tension snaps to the right (two red arrows), thus advancing the center seconds
wheel for one increment/sec.
I knowmy explanation is quite clumsy - but I hope it will at least not add more confusion :-)
Best regards
Suitbert