Ronda Caliber 509 Dial Side Big Date Datewheel

Why Some Big Date Movements Do Not Jump Directly From 31 to 01

Why doesn’t my double digit big date watch change from 31 to 01, is it broken or fake?

It’s because the Swiss calendar has 40 days in a month. Just kidding! Read below to learn more about the big date complication that seemingly gives you more time than everyone else….

When it comes to calibers with a big date complication, one of the most common questions is about the functionality of the date change. On some big date movements, such as Ronda caliber 509 and caliber 519, the date does not changeover from the 31st of the month directly to the 1st. There is nothing to be concerned about and it doesn’t mean your watch is fake.

For example, the date on the Ronda 509/519 goes from 31 to 32, 33, 34, 35, 36, 37, 38, 39, 00… then to 01. The reason for this is because in order to obtain the look of the big double digit date display, the movement uses two date wheels instead of one.

Ronda officially acknowledges this as part of the movement’s functionality by stating: “Big date without direct change from 31–01”.

Ronda Caliber 509 Dial Side Big Date Datewheel

How it works:

As shown in the image above, both date wheels have the same size of font, but the diameter of each wheel is different: The inner wheel is for the first digit. This wheel only needs 0, 1, 2, and 3. There are a total of 12 digits with the group of numbers repeated 3 times around the datewheel.

The outer wheel displays the second digit. There are 20 digits with numbers spanning from 1 to 0 (10), repeated twice around the datewheel. A traditional datewheel would look similar to this but with smaller text numbered from 1-31.

The outer datewheel advances once every 24 hours – the same as a regular date complication. The inner datewheel only advances once every ten times the outer rings advances. Therefore, when the date gets to 31, the movement still needs to cycle through the rest of the numbers until it reaches zero again on the outer datewheel.

Do All Big Dates Do This?

Some big date calibers function differently than others. The Shanghai Watch Company caliber 2L27 is a good example. This automatic movement features a big double digit date at 12:00, but instead of two concentric datewheels within each other, it has two smaller datewheels side-by-side.

Ingersoll Caliber 735 Shanghai 2l27 Big Date

As you can see above, there are some similarities to the quartz Ronda movement mentioned above. The left datewheel only has 0, 1, 2, and 3… but in this example, the numbers are only repeated twice and with 2 extra 0s.  The right wheel is numbered from 0 to 9, with the numbers only printed once. In order to achieve a seamless 1-31 date flipping experience, the mechanics are more complicated. Instead of describing the process with words, watch the video below…

Do you have a double digit big date watch? Tell us about it in the comments below…

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Gregory H.
Gregory H.
1 year ago

Very interesting! On the video I can actually see the gearing that makes it know when to jump. Like when you were at 01, 02, 03 ,04 then the left one jumped to a second 0 for 05,06,07. Some of those gear teeth are shorter to make it do that. Had no idea!

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