ETA Caliber F06.115

Manufacturer	ETA
Caliber Number	F06.115
Replaces Calibers	ETA 955.112, F06.111
Type	Quartz, battery-powered
Linges	11.5”’
Overall Diameter	25.6mm
Casing Diameter	26.20
Height	2.50mm thick
Jewels	Three (3)
Frequency	32,768 Hz
Battery Cell Number	371 (SR920SW) or 395 (depends on the watch case design)
Battery Life	~68 to 94 months (depending on the battery’s mAh)
Hand Count	3
Hand Sizes	1.20mm / .70mm / .20mm
Functions	Central hours; central minutes; central seconds (also without seconds); date at 3:00
Other Features	Low battery indicator (EOL)
Hacking Seconds?	Yes
Country of Manufacture	Switzerland, Swiss made (V8)
Known Models	2021 Tissot PRX ref: T137.410.11.041.00 (blue), T137.410.11.051.00 (black), T137.410.11.031.00 (silver); (Add your watch to the comments below…)

The ETA caliber F06.115 is an affordable Swiss quartz movement with 3 jewels. This caliber is part of ETA’s entry level Trendline series of movements. Based on ETA official tech documents, this caliber has been on the market since at least September 30, 2019.

HeavyDrive:

This caliber is equipped with ETA HeavyDrive which is essentially a sophisticated anti-shock technology for a quartz watch. In ETA’s own words:

“HeavyDrive technology enables intelligent shock management for the second’s hand and is opening up new possibilities for hand design.” –source

EOL:

You may see this movement listed as an EOL. In fact, Tissot even lists “Quartz EOL” below the watch pic on their PRX page (https://www.tissotwatches.com/en-us/collection/all-our-watches/t-classic/tissot-prx.html). EOL stands for end of life. This is a low battery indicator that is built into the circuit board to cause the second hand to jump every 4 seconds when the battery is low on juice.

Battery Life:

The F06.115 has rather long battery life when using a higher mAh cell. When using a 40 mAh cell, the battery life can be up to 68 months. With a 55 mAh battery cell, the battery lasts up to 94 months.

Note that you cannot simply install a high mAh battery unless your watch is designed to handle the increased thickness. The 371 cell has a diameter of 9.5mm no matter what the mAh is, but the 40 mAh cell is only 2.1mm tall compared to the 55 mAh cell at 2.7mm.

How to Change the Battery:

The F06.115 takes battery number 371 (aka SR920SW) low drain 1.55 V.

Replacing the battery on your F06.115 watch is very straightforward. As pictured, place your tool between the battery and the arm that holds it in place (#2 in the image below). Gently pry the arm back and the battery should lift up. Be careful not to bend of break off the arm that holds the battery in place!

To install the new battery, do the process in reverse, but make sure the battery is placed under the lip first (#3 in the image above). If you install a new battery and the watch doesn’t function properly, it’s possible that the battery is bad. Always try a new battery before giving up.

Crown/Stem Removal:

To remove the crown, look for the stem release hole on the movement near the crown There is a small arrow pointing to it. Putting the crown to date setting position should reveal a button in the hole that you can gently press with your tool to release the stem. Do this carefully and do not press too hard. If you damage the stem release mechanism, there doesn’t seem to be a way to fix it since it’s encased in plastic.

Date Changing:

The F06.115 has a quick set date feature with the crown in the second position. The date flip on a running watch is considered semi-instantaneous. Therefore, don’t be alarmed if there is lag from the time the date engages and flips over at midnight. The total time is takes for the date to flip can be up to an hour.

If the date on your watch doesn’t flip when the hands pass midnight, it doesn’t necessarily mean your watch needs serviced or has an issue, it could simply be how the hands were installed by the manufacturer.

Replacement Price:

At the time of this post, replacement prices for the F06.115 are unavailable. It appears that parts resellers are not stocked with the F06.116 yet. This were found online in the range of $20.95 – $29.80 USD.

Pros:

• Decent battery life.
• Gilt brass main plate and bridges.
• Relatively low cost to replace.
• HeavyDrive shock protection.

Cons:

• Some complaints about second hand having too much play and not lining up.
• Comment below if you have experienced any cons with this movement.

Examples of watches with caliber F06.115:

Additional Resources:

• ETA HeavyDrive press-release