The Ernst Benz Chronolunar Officer GC10381 is a large, 47 mm automatic chronograph with a full calendar, moon phase and 24-hour display. Its appeal is the unusual amount of information and mechanical functionality on the dial; its main trade-offs are the substantial case size, busy display and a manufacturer warning that makes calendar adjustments especially important to handle correctly. Ernst Benz displays a price of $7,625 for the reference, but that listing is not a guarantee of stock or a measure of what a buyer will pay.
What the Chronolunar Officer GC10381 does
GC10381 brings together an automatic chronograph and calendar indications. Hours, minutes and subsidiary seconds share the dial with day, date, month, a 24-hour indication and moon phase, as well as chronograph hours, minutes and central seconds. Ernst Benz says the day, month and moon phase show through dial apertures; a crescent-pointed central hand indicates the date. The 24-hour indication is on a subsidiary display. Ernst Benz’s product page identifies this exact reference as the black-dial version with steel luminous applied numerals. The Officer line also includes other dial and numeral finishes, so specifications for another reference should not be assumed to apply to GC10381.
GC10381 specifications
| Specification | GC10381 |
|---|---|
| Case | 47 mm polished stainless steel, with exhibition back |
| Crystal | Domed sapphire with anti-reflective treatment on the underside |
| Crown | Knurled crown with double O-ring seals |
| Dial | Black, with steel luminous applied numerals |
| Movement | Automatic Valjoux 7751; Ernst Benz lists Incabloc, a Glucydur balance and a Nivarox alloy hairspring |
| Functions | Hours, minutes, subsidiary seconds, day, date, month, 24-hour display, moon phase, and chronograph hours, minutes and central seconds |
| Strap | Handmade alligator, reference 22-20R-A.010 |
| Water resistance | 5 atmospheres / 50 m / 165 ft, as listed by Ernst Benz |
These are manufacturer-published specifications, not independent performance measurements. Ernst Benz describes its watches as designed, developed and produced in Switzerland; that is the manufacturer’s description. The GC10381 product page is the reference for the listed details.
How large is it, and is the dial easy to read?
The 47 mm case is a defining part of the watch, not a small detail. Whether it fits comfortably depends on the wearer’s wrist and preferences; case diameter alone cannot settle that question. If possible, try the watch on, or compare its diameter and overall shape with a watch you already find comfortable. The many calendar and chronograph indications also make this a visually dense dial, even though the applied numerals are luminous.
#1 Best Overall
- Orient Bambino
- Set Includes: Main unit, box,
- Drive Type: Mechanical (self-winding, hand-winding)
- Time accuracy: +25 seconds to -15 seconds per day
- Country of Origin: Thailand
In a hands-on review published May 8, 2012, John Biggs of TechCrunch called it a “huge ‘officer-style’ chronograph” and said the 47 mm case felt almost too large on his wrist. He found the dial surprisingly readable, but noted that the unlumed sub-register hands were difficult to use in total darkness. Those are one reviewer’s observations at that time, not a universal fit judgment or a current test. Read the TechCrunch review.
Read the setting warning before adjusting the calendar
Ernst Benz warns that using the day/date adjustment while the hour hand is between 8 p.m. and 2 a.m., or adjusting the moon phase between 8 p.m. and 6 a.m., can seriously damage the calendar gears; the manufacturer says that damage is not covered under warranty. The intervals refer to the watch’s indicated time. Do not use quick-adjust functions during those windows.
Rank #2
- 59 teeth gear for 29 ½ Days MoonPhase Display
- BlueGold Stone Dial
- Perlage Movement Polished and Engraving
- Big Date Indicator
- Exhibition Case Back Cover
“PLEASE BE ADVISED: engaging the Day/Date function when the Hour Hand is between 8pm – 2am and engaging the Moon between 8pm – 6am can cause serious damage to the calendar gears of the internal movement and such damage is not covered under warranty.”
For winding, setting the time, and correcting the day, date or moon phase, follow the instructions for this watch rather than generic advice for calendar watches. The manufacturer’s Chronolunar Valjoux 7751 operating instructions describe crown positions and the day-adjustment pusher. If you do not have the watch’s manual, obtain the correct instructions before making a calendar correction.
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Rank #3
- 59 teeth gear for 29 ½ Days MoonPhase Display
- Gold Swan Neck
- Column Wheel Chronograph
- Blue steel screws
- Exhibition Case Back Cover
Price and availability: verify the exact reference
Ernst Benz displays $7,625 for GC10381 on its product page. That is the manufacturer’s displayed price at the time represented by the listing, not proof of a completed sale, guaranteed inventory, a discount, or the value of a pre-owned watch. Check the manufacturer listing for current price and availability. Provident Jewelry also lists GC10381 and corroborates key specifications, but retailer stock and prices can change. Check its listing directly.
When considering a listing, confirm that it is actually reference GC10381 rather than a related Chronolunar Officer model. For a pre-owned example, assess condition, service history, warranty and seller terms separately; the new-watch specification page does not establish those details. The manufacturer specifies strap 22-20R-A.010 for this reference, but that alone does not confirm that a particular replacement strap will fit. Verify dimensions, end fitting and buckle compatibility before buying one.
Rank #4
- 59 teeth gear for 29 ½ Days MoonPhase Display
- Power Reserve Indicator
- Perlage Movement Polished and Engraving
- Exhibition Case Back Cover
- 12 Months Warranty
Who should consider it?
GC10381 is most compelling for someone who wants a mechanical chronograph with multiple calendar indications and likes the prominent, information-rich dial. It is a less natural choice for a buyer seeking a compact watch, a minimalist display or calendar adjustments that can be made without paying close attention to the manufacturer’s timing warning. Compare alternatives by case fit, legibility and lume, movement and complications, calendar-setting method, water-resistance rating, strap compatibility, condition and service history, and verified total price. The listed 50 m rating is a specification; it should not by itself be treated as a promise of suitability for a particular activity.
Quick Recap
Best Value
- Set Includes: Watch, box, and warranty card included RPA2023 Drive System: Mechanical (hand winding and self-winding)
- Accuracy: Daily difference + 25 seconds to -15 seconds
- operating time: 40 hours RPA2023 Country of Origin: Japan (Made in Japan)
Product prices and availability are accurate as of the date/time indicated and are subject to change. Any price and availability information displayed on Amazon at the time of purchase will apply.
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