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ETA 2824-2 vs. Miyota Cal 821a

May 27, 2013

The majority of watchmakers don’t have their own in-house movements. They usually purchase their movements from ETA, Citizen, and other firms. This became common after the popularity of quartz-powered watches in the seventies and eighties when everyone wanted a quartz watch for its unparalleled precision, reliability, and affordability, forcing surviving watchmakers to start buying movements rather than developing their own.

Two of the most popular watch movements found in several watch brands today are the Swiss ETA 2824-2 and the Miyota Cal 821a. Both are excellent movements and provide accurate and reliable mechanics for your favorite timepieces. We see the ETA 2824-2 movement in many watch brands such as a.b.art, Altanus, Cartier, Junkers, LACO, Maurice Lacroix, TAG Heuer, Tissot, and Zeppelin. While the Miyota movement is common in lower-priced watches (around $500 or less) from brands like Junkers, Invicta, LACO, and many others.

These two movements are quite similar but have some significant differences:

Both movements are automatic, using a winding rotor to power the mainspring as you move around during the day.
Power reserve: Automatic movements have a built-in power reserve so the watch can keep running while not in use. The ETA offers a very respectable 40 hours of reserve, but the Miyota trumps it in this category with 45 hours. However, the ETA utilizes ball bearings for the rotor, making it more efficient at winding the watch and requiring less wrist time per day to keep it running.
Jewels: Both movements utilize synthetic rubies in their constructions, with the ETA 2824-2 being a 25-jewel movement and the Miyota featuring 21 jewels.
Beat Per Hour (BPH): The ETA 2824-2 performs at 28,800 beats per hour (8 beats per second or 4Hz), while the Miyota 821a beats at 21,600 BPH (6 beats per second or 3Hz). This means the ETA movement is smoother and more accurate due to its higher frequency. However, both movements exceed the traditional standard of 2.5Hz (18,000 BPH) for mechanical watches.
Direct second-hand drive vs. Indirect second-hand drive: Perhaps one of the most significant differences between these two movements.

The ETA 2824-2 movement features a direct second-hand drive, meaning the second hand will not stop for moments due to wrist movements.

The Miyota 821a comes with an indirect second-hand drive, causing the second hand to “pause” due to strong wrist movements. This "pause" is caused by the slight play within the teeth of the third wheel in the train that turns the second hand. On average, the maximum pause time equates to 2 seconds, but typically the movement will pause for less time. This is primarily an aesthetic issue, as the indirect second-hand drive doesn't affect the watch's accuracy.

Hacking second hand: The ETA 2824-2 is a hacking movement, meaning the second hand stops while the time is being set; on the other hand, the old versions of the Miyota 821a did not, however the newer version is also a hacking movement.
Shock resistance: Both watch movements offer excellent shock resistance. The ETA uses Incabloc, a method that allows jewels to float when the watch is bumped. The Miyota employs a proprietary shock resistance system known as the Parashock.