At a special training session with A. Lange & Söhne last year, head of the Zeitwerk manufacturing division, Robert Hoffmann, explained a few things you should know about the new Zeitwerk Date and Zeitwerk today.

It’s got a long mainspring.

The Zeitwerk’s design, having to constantly turn the minute and hour discs minute upon minute, hour into hour, consumes a lot of energy. That’s not surprising or new. This is especially true at the end of each hour, when all the discs have to turn. The older edition of the Zeitwerk has a mainspring that keeps the watch running for 36 hours, but the watchmakers at Lange wanted to double that. The solution was to create a double barrel solution, running in parallel, stacked one on top of each other, and each mainspring is now slimmer but with greater tension and longer; in fact, it’s the longest mainspring the brand has ever developed.

It’s got a more efficient power delivery.

Gear trains are like any other energy transmission system — the more you eliminate energy wasted, the longer power lasts, just like fuel-efficient automobiles. The Zeitwerk Date has a smaller balance spring which is also lighter. It also possesses a thinner remontoire spring compared with older models of the Zeitwerk to regulate the power flow from the mainspring to the escapement. All these means there’s less energy needed to keep the engine of the watch running, and thus the watch can run for longer without winding.

Closeup of escapement and remontoire point
There’s a new pre-tension spring in L043.8 calibre.

The time when the Zeitwerk’s display consumes the most energy is when multiple displays need to move, say every 10 minutes, or every hour on the hour. Not only does this impact the power resource, it can also cause a dip on the amplitude of the escapement, although it’s not a significant one. To prevent this, the brand has introduced a pre-tension spring that works on the decimal minute display. As the time progresses from minute one to nine on the snail cam, the pre-tension spring is loaded. At the decimal jump, the system gets an extra boost in energy to keep all the display jumps aligned, and also at the end of the day when the date needs to instantaneously jump at midnight. This means that even through towards the end of the power reserve, there’s no discernible change in performance.

The windbreak in the movement ensures power is balanced.

Since there are now two mainsprings in the movement, that’s a lot of juice to start when the mainsprings are fully wound. It serves to basically absorb the excess energy from the mainspring when only smaller amounts of energy are required, such as at a single minute jump when the reserve is full by running a little longer.

The digital display incorporates springs to ensure a more precise jump.

Across the standard Zeitwerk, a little quirk that owners used to see was a slight pre-jump in the disc, as the indicator was about to switch from minute to minute. Now, the displays are fitted with little springs, so that they are always in the same position when the display shifts. It was designed to bring greater precision to the jump, but also makes it easier to adjust and assemble. It also results in a smaller drop in amplitude when the displays jump and further saves energy in the system, which contributes to the longer reserve.