Then there is the method of engaging the chrono drive. As recently emphasised over the new chronograph from JLC, the Cal 75x,
"There are 3 main types of coupling, Lateral, Vertical or sliding Pinion, Vertical Coupling is a signature for high-end chrono. Test shows Vertical Clutch system has the advantages of (1) No hesitation of the chrono seconds hand at start, (2) much higher shock resistant and (3) The rate of balance wheel remain unchanged at start and stop, making accurate time recording possible"You can see the vertical clutch system in the Lemania 5100 in this excellent pictures taken from the extensive gallery of Lemania 5100 (and Omega 1045) movement photographs maintained by Sergio Lorenzon at his very useful WatchScape site.
Lemania 5100: Vertical clutch is the gizmo with the 3 pointed star (that's the clutch spring).
Note also the chrono seconds heart shape cam that there are often problems with getting to reset to '0'.
That big 'Y' shape below is its reset hammer.
Finally, there are two methods of controlling chrono operation: either cam as you can see below in my Lemania 1877 movement or by column wheel.
Lemania 1877 in a Sinn 903. The cam is the little gizmo at 9 o'clock that looks like an apostrophe with a screw head in the middle!
JLC Cal 75x: The column wheel is at 2 o'clock.
Now 'column wheel' is considered 'the best'. My question is what is the definition? It's certainly got to be a rotary device rather than to-and-fro. It requires high points and voids to guide the movement of the different levers which press a column or fall in a void. So, does the rotary device at 11 o'clock in the picture below qualify as a column wheel?
Lemania 5100: Column wheel at 11 0'clock or rotary cam?