ETA (Valjoux) · ETA A05.H31 chronograph

Tissot PRX Chronograph, Heritage 1973 and PRS 516 power reserve: inside the Valjoux A05.H31

The Tissot PRX Automatic Chronograph, Heritage 1973 and PRS 516 Automatic Chronograph run on the Valjoux A05.H31, a long-reserve update of the Valjoux 7753. From full it runs for about 60 hours, or two and a half days.

Updated September 2026 · Based on manufacturer specs, published reviews and watchmaker/owner reports

Watches that use the A05.H31

The A05.H31 is a Swatch Group chronograph, so you'll find it in Tissot's mechanical chronographs rather than across the industry like the Valjoux 7750. Tissot usually calls it simply "Valjoux" or "automatic chronograph" on the dial and in its catalog. Two things trip people up: some Tissot chronographs with a similar look use a sister calibre, the A05.231, and the Seastar 1000 Automatic Chronograph uses a completely different movement.

Specs at a glance

History and where it came from

The Valjoux 7753 is a variant of the famous 7750 with the counters rearranged into the symmetrical 3-6-9 layout. It's a proven design, but at around 42 to 48 hours it has a short reserve by modern standards. In the 2010s Swatch Group updated it as the A05 family, the same way it had turned the ETA 2824 into the 80-hour Powermatic 80.

The A05.H31 keeps the 7753's architecture and 4 Hz beat, but a longer-running mainspring and reworked gear train take the reserve to 60 hours. SJX, in its hands-on with the PRX Chronograph, noted that it keeps a standard smooth balance and Etachron regulator, so the change is about endurance rather than a new regulating system. The sister A05.H21 is the 7750-layout, day-date version. Hamilton's H-21 applies the same idea to the 7750.

Tissot used the A05.H31 in the PRS 516 and Heritage 1973 before it reached a much bigger audience in 2022 with the 42 mm PRX Automatic Chronograph.

Accuracy in the real world

Tissot doesn't publish an accuracy spec for the PRX Chronograph or Heritage 1973. The 7753 family comes in grades from Standard up to chronometer, and the A05.H31 in these Tissots isn't sold as a chronometer. Owner reports on watch forums are generally in the range you'd expect from a well-set 4 Hz movement, usually within a handful of seconds a day, with the usual variation between examples.

The advantage over the Powermatic 80 is regulation. Because the A05.H31 has a conventional regulator index, any competent watchmaker can adjust it. If your PRX Chronograph runs fast, it's a quick job rather than a specialist one.

As with any chronograph, running the chronograph draws extra power and can lower the balance amplitude slightly. Leaving it running all day shortens the reserve and adds wear.

Reliability and servicing

The 7750 and 7753 are among the most-serviced chronographs in the world, and the A05.H31 inherits that robustness. Monochrome's long look at the 7750 family found that most reported problems came from mishandling rather than design faults.

• Service cost. A chronograph service costs more than a time-only one because there are more parts to clean and adjust. Tissot's own service network is the easiest route.
• Parts. Much of the chronograph works is shared with the 7750 family, which watchmakers know well. Parts specific to the A05, like the mainspring, come through Swatch Group's network.
• Checking a used one. Start the chronograph, let it run a few minutes, then stop and reset. All hands should snap back to zero every time.

Quirks worth knowing

• The wobble. Like the 7750, the rotor winds in one direction and spins freely in the other. You may feel it swing on the wrist. That's normal.
• Recessed date corrector. On the PRX Chronograph, the date is set with a recessed pusher at 10 o'clock that needs a pointed tool, not the crown. It's the most common owner complaint about the movement.
• Date placement. In the three-register PRX, the date sits between 4 and 5 o'clock. On the two-register PRS 516 it moves to 6.
• Thickness. A 7753-based chronograph is tall. The PRX Chronograph is 14.5 mm thick, much chunkier than the time-only PRX.
• Date danger zone. Avoid correcting the date between roughly 9pm and 3am. Here's why.

How it compares

• Valjoux 7750: the parent family, used by far more brands, but usually with only 42 to 48 hours of reserve.
• Hamilton H-31: Hamilton's 7753-based equivalent with 60 hours and a Nivachron balance spring, in the Intra-Matic Auto Chrono.
• Hamilton H-21: the 7750-layout, day-date sibling with the same 60-hour reserve.
• Tudor MT5813: a column-wheel chronograph with 70 hours in the Black Bay Chrono, at a much higher price.

Living with the 60-hour reserve

Sixty hours is long for a chronograph, but it's not a full weekend. Take your Tissot PRX Chronograph off at 6pm on Friday and it will still be running on Sunday afternoon, but it will probably have stopped by Monday morning. Run the chronograph on Saturday and it stops sooner.

A stopped chronograph is more annoying to restart than a three-hander, because the PRX's date needs a tool to correct. It's the kind of watch worth tracking if it's one of several you rotate. Watch Winder counts down the reserve for each watch you own and reminds you before it stops, so you can wear it or give it a few turns of the crown first. To check a particular weekend, try the "Will my watch stop?" calculator.

A note on the numbers: Tissot quoted 60 hours when the PRX Chronograph launched, and most reviews still do. Some current Tissot product pages list 65 or 68 hours, and newer references also mention a Nivachron balance spring. We use 60 hours as the safe figure until it's clear which pieces have the longer spec.

Verdict

The A05.H31 is the sensible modernization of a workhorse. It keeps everything that made the Valjoux 7753 reliable and easy to service, and adds enough reserve that a PRX Chronograph or Heritage 1973 survives a day or two in the drawer. It's thick, the rotor wobbles, and the PRX's recessed date corrector is a nuisance, but as a Swiss automatic chronograph at Tissot prices, it's hard to argue with.

FAQ

How long does a Tissot PRX Chronograph run off the wrist?

About 60 hours from full, which is two and a half days. Some newer Tissot product pages list up to 68 hours, but plan on 60 to be safe.

What movement is in the Tissot PRX Automatic Chronograph?

The Valjoux A05.H31, a Swatch Group update of the Valjoux 7753 with 27 jewels, a 4 Hz beat and a longer reserve.

Does the Tissot PRX Chronograph hack and hand-wind?

Yes. The seconds stop when you pull the crown to set the time, and you can wind it by hand through the crown.

Does the Tissot Heritage 1973 use the same movement as the PRX Chronograph?

Yes. Both use the Valjoux A05.H31 with a 60-hour reserve, in very different cases.

Does the Tissot PR516 Automatic Chronograph use the A05.H31?

No. The newer PR516 Automatic Chronograph uses the closely related A05.231, which has no date. The earlier PRS 516 Automatic Chronograph used the A05.H31.

Why does my Tissot PRX Chronograph wobble on the wrist?

The rotor only winds in one direction and spins freely in the other, as on the Valjoux 7750. It's normal unless you feel scraping or grinding.

Is the A05.H31 better than the Valjoux 7750?

For daily use, mostly yes: it keeps the same robust chronograph design but runs about 60 hours instead of roughly 42 to 48.

Sources

• SJX: Hands on, Tissot PRX Automatic Chronograph
• Monochrome: Hands-on with the Tissot PRS 516 Automatic Chronograph
• Monochrome: First look, Tissot PR 516 Automatic Chronograph (A05.231)
• Grail Watch Wiki: ETA A05
• Tissot: PRX 42mm Automatic Chronograph product page

Watches we've reviewed with the ETA A05.H31 chronograph

• Tissot PRX Automatic Chronograph review

Keeping it running

• On an average day an automatic gains roughly 4 hours of reserve per hour on the wrist, so about 15 hours of wear fills the ETA A05.H31 chronograph. Desk days charge more slowly.
• Most automatics can also be wound by the crown. If yours has stopped, a few dozen turns gets it going before you put it on.
• Off the wrist it stops about 60 hours after it was last full. Stopped sooner?
• On a watch winder, start at about 800 turns per day, clockwise. Winder settings for every movement.
• If it does stop, don't set the date between 9pm and 3am. Check if it's safe.

All ETA movements

Never let it stop

Watch Winder counts down the reserve of every watch you own and reminds you before one stops. It already knows the ETA A05.H31 chronograph: type your watch's name and the reserve fills itself in.

Manufacturer's published figure. Real reserve varies with the watch's age and service; check your manual.