Black/Cyber Weekend Watches
Ronda Caliber 509s

Ronda Caliber 509

Ronda Caliber 509

Caliber Number509
Battery Number371 (1.5 V)
Battery Life
45 months
Current Consumption
1.28 μA to 1.85 μA (max)
Hand Sizes120/70/20
FunctionsCentral hours, central minutes, central seconds, big date at 3:00
Country of ManufactureSwitzerland or Other (Swiss Parts)
Known Models
Mondaine EVO2 Big Date (Add your watch to the comments below…)

The Ronda caliber 509 is three hand quartz watch movement with a big double digit date at 3:00. This movement is part of the Powertech line. There are two versions of this caliber: Swiss made and Swiss parts. Both versions are nickel plated with one jewel. It is considered a repairable movement.

Big Date Changeover:

One of the most common questions about this caliber is the functionality of the date change from the 31st of the month to the 1st. The date on the Ronda 509 does not flip from 31 to 01. It goes from 31 to 32, 33, 34, 35, 36, 37, 38, 39… then to 01. The reason for this is because in order to obtain look of the big double digit date readout, the movement uses two date wheels instead of one.

There is nothing to be concerned about and it doesn’t mean your watch is fake. Even Ronda officially acknowledges this as part of the movement’s functionality by stating: “Big date without direct change from 31–01”.

How it works:

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. These numbers are repeated 3 times in a circle. As for the outer digit, it goes from 1 to 0 (10), repeated twice.

The inner datewheel only advances once for every nine 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.

Ronda Caliber 509 Dial Side Big Date Datewheel

Big Date Location:

The most common configuration of the big date on the Ronda caliber 509 is two digits side-by-side at 3:00. It is also possible for a watch design to feature the double digit date at 6:00 with the numbers stacked on top of each other. A tilted big date is also possible at 4:00. These positions are not exactly interchangeable. For example, the 6:00 date will need different datewheels with the numbers printed vertically.

Ronda caliber 509 vs 519

There is a similar Ronda caliber 519 which has the same layout with a double digit date at 3:00. The main difference is that the 519 is a larger movement with the diameter being 11.5”’ (25.60mm) vs the 509 measuring 10.5”’ (23.3mm). Both movements are 3mm tall.


According to Ronda, the caliber 509 should keep time within -10/+20 seconds per month with an operating temperature of 0 to 50 degrees Celsius.

Power Reserve

A fresh battery (cell 371) should last for 45 months. This caliber has a power saving (hacking) function that stops the second hand when the crown is pulled out. Doing this will reduce power consumption by about 70%.

Caliber Number Location

Ronda does not stamp the metal part of this movement with the caliber number, instead, you can find a reference on the outer plastic part of the movement.

How to change the battery

There is a metal locking mechanism for the battery that just uses tension to hold it into place. Gently put your tweezers or other tool in the hole and slide it over – not too hard and not too far. The battery will pop out like in this video. Do not remove the screw. (The image below is of a similar caliber with the same battery changing process.)

Ronda Caliber 513s Battery Replacement

Stem Removal

To remove the crown/stem, find the hole with the arrow. While the crown is in position 0, pressing this with your tweezers or other tool will allow the stem be unlocked so you can pull it out. (The image below is of a similar caliber with the same stem removal process.)

Ronda Caliber 513s Crown Stem Removal

Replacement Prices

At the time of this post, replacement prices for this watch movement were found in the range of $9.45 – 19.99 USD.

In Ronda’s words:

  • Repairable metal watch movement
  • Power saving mechanism with pulled out stem: Reduction of consumption approximately 70%
  • Interchangeability: All versions 10½”’ with same movement height 3.00 mm and stem height 1.50 mm
  • Very powerful stepping motor
  • Big date with quick change

Additional Resources:

Venus Caliber 178
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