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Tissot’s A05.231 is an updated take on the Valjoux 7750, not a new chronograph architecture. It retains the 7750’s cam-and-lever controls and oscillating-pinion clutch, while adding a stated 68-hour power reserve, a Nivachron hairspring and a variable-inertia balance. In the Tissot Telemeter 1938, the movement also brings a bi-compax display and revised construction and finishing.
What changed between the 7750 and Tissot A05.231?
The A05.231’s most tangible change for an owner is its longer stated power reserve: 68 hours, compared with 54 hours in ETA’s current specification for the standard Valjoux 7750. Tissot also updates the regulating system and adds a Nivachron hairspring for improved resistance to magnetic effects. The underlying automatic chronograph mechanism, however, remains recognizably a 7750.
| Feature | Valjoux 7750 | Tissot A05.231 |
|---|---|---|
| Power reserve | 54 hours typical, according to ETA’s current specification. | 68 hours, as reported for the A05.231 by Monochrome in 2022. |
| Dimensions | 30.00 mm diameter × 7.90 mm high, according to ETA’s current specification. | 30.40 mm diameter × 7.94 mm high, as reproduced by Monochrome in 2022. |
| Jewels | 25, according to ETA’s current specification. | 29, as reproduced by Monochrome in 2022. |
| Frequency | 4 Hz (28,800 vibrations per hour), according to ETA’s current specification. | Not stated in the cited A05.231 specification reproduced by Monochrome in 2022. |
| Winding and chronograph | Automatic, unidirectional winding; cam-operated chronograph with an oscillating-pinion clutch, according to ETA’s specification. | Automatic 7750-derived cam-and-lever chronograph with an oscillating-pinion clutch, as described by Monochrome in 2022. |
| Balance and hairspring | Conventional regulation, contrasted with the A05.231’s updated system in Monochrome’s 2022 account. | Variable-inertia balance and Nivachron hairspring, as described by Monochrome in 2022. |
| Display example | Day/date and 60-second, 30-minute and 12-hour chronograph counters, according to ETA’s current specification. | The Telemeter 1938 uses a bi-compax layout, as described by Monochrome in 2022. |
The figures compare ETA’s current standard 7750 specification with the A05.231 figures reported by Monochrome in 2022; they are not a same-date, laboratory side-by-side test. The 68-hour figure is a stated reserve, not a guarantee of identical real-world runtime in every watch.
Why does the A05.231 run longer?
The A05 family is specified at 68 hours of power reserve. That is 14 hours more than the 54-hour typical reserve in ETA’s current 7750 specification. In practical terms, the longer reserve gives the watch more time off the wrist before it stops; the Telemeter 1938 may remain running through a weekend depending on when it was last fully wound and how it is used.
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Monochrome’s 2022 account describes this as an upgrade to the established Valjoux architecture rather than a wholesale replacement. The reserve improvement is the easiest change to quantify from the available specifications, but the stated numbers alone do not establish how much reserve a particular watch will deliver in daily wear.
How do the hairspring and balance improve the movement?
Nivachron hairspring
The A05.231 uses a Nivachron hairspring. Magnetic fields can affect a conventional hairspring by magnetizing it and causing its coils to stick together, which can disrupt timekeeping. Replacing it with Nivachron is intended to improve precision and reliability in environments with everyday magnetic sources, as Monochrome explains.
No quantified magnetic-resistance rating or laboratory result for an individual A05.231 watch is established by the cited specifications. The feature supports a claim of improved anti-magnetic performance relative to the conventional arrangement, not that the watch is immune to magnetic fields.
Rank #2
- COSC Certified Chronometer
- Case Size: 39.00 mm, Band Width: 20 mm, Case Thickness: 10.98 mm
- Automatic movement, 316L solid stainless steel bracelet, Roman dial type, Date
- Water-resistant up to a pressure of 10 bar (100 m / 330 ft): suitable for short periods of recreational swimming and showering, but no diving or snorkeling.
Variable-inertia balance
The balance uses asymmetrical screws on its spokes for rate adjustment. A watchmaker can regulate it by changing the balance’s inertia, rather than moving a conventional index to alter the active length of the hairspring. Monochrome describes this as a variable-inertia arrangement that omits the traditional index.
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1Fix the driver behind crashes, sound loss and screen glitches2Clear out junk files and repair common Windows errors3Scan for outdated or missing drivers - takes under a minuteWhat remains the same about the 7750 chronograph?
The A05.231 retains a cam-and-lever chronograph and an oscillating-pinion clutch. It is therefore not a column-wheel chronograph, nor a complete redesign of the 7750. The architecture that starts, stops and resets the chronograph remains rooted in the original system; the update is concentrated in reserve, regulation, materials and construction.
That distinction matters if you are comparing chronograph operation rather than just specifications. Tissot has modernized an established mechanism, but the available information does not establish a different pusher feel or a change to column-wheel-style actuation.
Rank #3
- Case Size: 38.00 mm, Band Width: 25mm, Case Thickness: 10.98 mm
- Automatic movement, leather strap, Index dial type, Date
- Water-resistant up to a pressure of 10 bar (100 m / 300 ft): suitable for short periods of recreational swimming and showering, but no diving or snorkeling.
What changed in the Telemeter 1938’s display and movement finish?
The classic 7750 specification includes day/date and chronograph counters for 60 seconds, 30 minutes and 12 hours. In the Telemeter 1938, the A05.231 is presented with a bi-compax layout rather than the familiar 12-6-9 counter arrangement associated with the 7750. Monochrome also reports revised bridge architecture and a metallic stop lever in place of the plastic part used in older versions.
The movement’s presentation is updated with industrial perlage and a personalized openworked rotor. These are refinements to the finish and appearance; they should not be mistaken for hand-finished haute horlogerie decoration.
Is the A05.231 a better 7750?
It is better equipped in specific ways: it has a longer stated reserve, Nivachron anti-magnetic protection, a variable-inertia balance, and revised construction and finishing. Those changes make the A05.231 a meaningful evolution for someone who values extra time off the wrist and modernized regulation.
Rank #4
- Case Size: 40.00 mm, Band Width: 12, Case Thickness: 10.93 mm
- Automatic movement, 316L stainless steel case, Index dial type, Date
- Stainless steel strap/bracelet, interchangeable quick release bracelet,butterfly clasp with push-buttons closure
- Water-resistant up to a pressure of 10 bar (100 m / 330 ft)
- 2 Year International Warranty
It is not a universal upgrade in every respect. The chronograph remains based on the same cam-and-lever and oscillating-pinion system, and the cited material does not quantify a magnetic-resistance rating or establish a performance test that would prove a particular watch is more accurate. The most accurate description is an evolutionary modernization of a proven automatic chronograph.
Which watches use the A05.231?
The Tissot Telemeter 1938 is the named watch associated with the A05.231 in Monochrome’s 2022 coverage. A movement reference alone does not confirm which other models or current production runs use it; model availability can vary by market and date.
For context, ETA describes the Valjoux calibre as a robust self-winding chronograph renowned for reliability and performance since its creation in the 1970s. The 7750 design dates to 1974; production paused during the quartz crisis and resumed in the mid-1980s, according to Monochrome’s historical account.
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