- ETA’s page for the 2824 movement has all the technical details
- ETA’s page for the 2892 movement has all the technical details
- ETA’s training tool has a step by step guide to disassembling the 2892 movement
- As the watch turn’s page comparing the movements includes a table with the characteristics of the different grades of each movement
The two movements have the same diameter of 25.6mm, the same frequency and the same functions (time with central seconds, date with corrector, time stop) and come in different grades including chronometre-grade for both. However, the 2892 is only 3.6mm thick, whereas the 2824 is 4.6mm, a whole millimetre more. The 2892 also has a slightly better power reserve of 42 hours versus 38 for the 2824. What I ask myself is why bother having two movements that do the same thing with the same level of accuracy when one is thinner than the other and has a longer power reserve? What’s the point of the 2824? The answer is production costs, which is why the 2824 tend to be in cheaper watches and with lower grades, whereas the higher grades are usually used for the 2892.
The actual movements pictured are Chinese clones, the ST1812 (ETA 2892) and ST2130 (ETA 2824). There are two different pairs of movements, which is why the same type of movement might be pictured with different types of finishing. Each movement can be found in different grades and that is therefore not a defining feature (see table in this article). In all the pictures, the 2892 clone is one the left. Clones are legal as the patents for both theses movements, that have been around for decades, have expired. Unlike fakes, they do not have any branding suggesting they are ETA movements.
As always, Walt Odets has some interesting insights on this topic.
Dial side
As you can see, there are no major differences in the design of the dial side of the two movements. I wonder why they don’t just use exactly the same keyless works and date mechanisms to keep the production costs lower. Is it to be able to say these are very different movements to justify the price difference?
Rotor
The rotor of the 2824 is secured by a single central screw and therefore can be taken off independently of the automatic bridge, the rotor of the 2892 is held by 3 screws from below and therefore can only be taken off once the automatic bridge has been removed from the movement. The 2892 has a larger central pivot, which some watchmakers say make it more durable and shock-resistant.
Automatic system
Both automatic systems used ETA’s double-layered reverser disks rather than the rocker system found in some Jaeger-Lecoultre and Nomos watches. I personally find the rocker system both more elegant in terms of engineering, but also more visually pleasing. The use of the double-layered disks might be because they are more durable than the rocker system (less coupling and uncoupling of wheels?) or because ETA does not want to have to use someone else’s patents (although the rocker system has been around long enough that the patent probably expired).
Main part of the movement
Visually, once the automatic bridge has been removed, the differences that are obvious is that the 2824 places the crown and ratchet wheels above the bridge and that it has a larger balance wheel.
Gear train
Both movements use the same layout with a central fourth wheel directly driving the seconds hand whereas the third wheel pinion reaches through the base plate and drives the friction wheel attached to the cannon pinion. In other words they have directly driven seconds and indirectly driven minutes. You can find more information about the different design possibilities linked to central seconds here. One difference is that the main wheel’s top jewel is part of the 2892’s barrel bridge, whereas it is part of the 2824’s gear train bridge.
Both mainspring barrels are the same size and so are both escape wheels. For all the other wheels, the 2824 ones are larger than their 2892 counterparts.
Balance wheel
The 2824 balance wheel is significantly larger and therefore has more inertia. This probably explains why despite have similar sized mainspring barrels, the 2892 has a longer power reserve.