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Casio G-Shock GA-2100-1A3ER Utility Black Resin Strap Watch - W17261
Ref. GA-2100-1A3ER
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Stepping up in the same dial colour
The GA-2100 arrived in 2019 and immediately acquired a nickname the internet settled on within weeks: CasiOak, for the way its octagonal case recalls the architecture of a certain famous Swiss sports watch, at a distance that is clearly deliberate. That reference is worn lightly — this is still unmistakably a G-Shock — but it gave the GA-2100 a following among people who had never bought a Casio before. The 1A3ER is the Utility Black variant, which keeps the all-black stealth aesthetic of the original and punctuates it with neon-green hands: a small intervention that reads very sharply against the matte dial. The Carbon Core Guard structure is what makes the proportions surprising. At 11.8mm thick, it sits flatter on the wrist than almost anything else in the G-Shock catalogue, and at 51 grams the whole watch — strap included — is light enough that it disappears during wear. The analogue hands can be swept aside on command to clear the digital display beneath them, which is a more useful arrangement than it sounds when glancing at world time or the stopwatch mid-activity.
- Reference
- GA-2100-1A3ER
- Brand
- Casio
- Collection
- G-Shock
- Case size
- 45.4mm
- Case thickness
- 11.8mm
- Case material
- Resin
- Case shape
- Octagonal
- Dial
- Black
- Crystal
- Mineral
- Movement
- Quartz
- Functions
- Day-date, Stopwatch, Countdown timer, Alarm, Backlight, World time, Dual display
- Water resistance
- 200m
- Bracelet / strap
- Rubber strap
- Strap colour
- Black
- Clasp
- Buckle
- Lume
- Luminous
- Retailer
- F.Hinds
Additional specifications
- Lug-to-lug
- 48.5mm
Learn more about Casio
Tadao Kashio founded Kashio Seisakujo in Tokyo in 1946 as a machine shop. The company's first success was a finger ring that held a cigarette, and its second was the 14-A of 1957 — the world's first all-electric compact calculator, which used solenoids rather than gears.
Casio entered watchmaking in 1974 with the Casiotron, a digital watch with an automatic calendar that knew the varying lengths of months. The company approached watches as an electronics manufacturer rather than a horological one, and that difference produced the G-Shock.
The G-Shock came from a single engineer, Kikuo Ibe, who broke a watch his father had given him and set out to build one that could not break. The specification was three tens: survive a ten-metre drop, ten bars of water pressure, and ten years of battery life. It took over two hundred prototypes, and the solution was suspending the module inside the case on a cushioned internal structure rather than mounting it rigidly. The DW-5000C shipped in 1983.
It became one of the most durable product designs in any category, adopted by militaries, emergency services, and skateboarders alike, and Casio has since added solar charging, radio and GPS timekeeping, Bluetooth, and full-metal and carbon variants.
Casio also produces the Edifice, Pro Trek, and Oceanus lines, and remains an independent Japanese public company.
- 1946
- Tadao Kashio founds the company in Tokyo.
- 1974
- The Casiotron is Casio's first digital watch.
- 1983
- The G-Shock DW-5000C survives Kikuo Ibe's three-tens brief.
- 1994
- The Frogman extends G-Shock to ISO dive certification.
Also in 7 collections
This watch appears in the Casio G-Shock range (84), Back in Stock (4,683), Watches 44mm and Over (827), Sports Watches (800), Watches Under £100 (589), Dive Watches (568) and All Black Watches (315).
Manufacturer’s guarantee
What the specifications mean
A watch built to be worn hard and got wet.
Strengths
- 200m water resistance, rated for actual diving
- 48.5mm lug-to-lug keeps the 45.4mm case wearable
- Luminous hands and markers for low light
- Second time zone for travelling
- Sits in the lower half of Casio's range as we list it
Worth knowing
- 45.4mm is a large watch with real presence
Casio G-Shock GA-2100-1A3ER Utility Black alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification | GA-2100-1A3ER | RW647AX9 | RYS07-4004-SET |
|---|---|---|---|
| Price | £100 | £99 | £100 |
| Case size | 45.4mm | 46mm | 46mm |
| Water resistance | 200m | 100m | — |
| Movement | Quartz | Quartz | Quartz |
| Strap | Rubber strap | Stainless steel bracelet | Mesh bracelet |
| This watch |
| Closely matched |
Your new watch
Frequently asked questions, and things you should know about this watch
Can I swim with it?
Yes. At 200m it is rated for swimming, snorkelling and recreational diving.
Water resistance explainedWill the glass scratch?
It can, over time. Mineral glass handles daily wear but will pick up fine scratches that sapphire would not.
Sapphire, mineral and acrylic comparedDoes it need a battery?
Yes. It is quartz, so expect a battery change every two to three years at a jeweller.
Quartz, automatic and solar comparedWill it fit my wrist?
Lug-to-lug is 48.5mm, which suits wrists from roughly 16.5cm (6½ inches) upward.
Lug-to-lug decides fit more than case diameter does.
How to size a watch to your wristIs it a men's or women's watch?
Listed as men's.
Cheapest place to buy
F.Hinds is the only UK retailer we track stocking this reference, so there is nothing to compare it against today.
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