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Casio G-SHOCK GBM-2100A-1A3ER Solar Green Dial Resin Strap Watch - W17567
Ref. GBM-2100A-1A3ER
Sits in Casio’s upper tier here — more premium than three quarters of the Casio watches we list, which start at £25.
Price range £25 to £919 across 136 Casio watches in stock.The GBM-2100 sits between two versions of the same idea. The original 2100 — the "CasiOak" — was built from resin throughout, which kept it light and unprecious. This variant keeps that bio-based resin core but wraps it in a finished stainless steel bezel, giving the octagonal case a harder edge and a surface that catches light differently from every angle. The green dial takes that further: the colour comes from vapour deposition rather than paint, which produces a metallic depth that shifts between olive and emerald depending on what it is near. At 11.9mm and 72 grams, it carries none of the bulk that a steel-bezelled G-SHOCK might suggest, and it will sit under a cuff without protest. The module beneath the analog-digital layout handles Bluetooth synchronisation to a paired phone for automatic time correction, which in practice means the ±15-second monthly tolerance of the solar movement becomes largely academic — the watch simply stays right. The double LED illuminates both the analog face and the digital window simultaneously, and the quick-release pins on the strap mean changing the black rubber band requires no tools and about thirty seconds.
- Reference
- GBM-2100A-1A3ER
- Brand
- Casio
- Collection
- G-Shock
- Case size
- 44.4mm
- Case thickness
- 11.9mm
- Lug width
- 16mm
- Case material
- Stainless steel
- Case shape
- Octagonal
- Dial
- Green
- Crystal
- Mineral
- Movement
- Solar
- Functions
- Date
- Water resistance
- 200m
- Bracelet / strap
- Rubber strap
- Strap colour
- Black
- Clasp
- Buckle
- Lume
- Luminous
- Retailer
- F.Hinds
Additional specifications
- Lug-to-lug
- 49.3mm
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), Stainless Steel Watches (3,109), Watches 44mm and Over (827), Sports Watches (800), Dive Watches (568) and Green Dial Watches (415).
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
- 49.3mm lug-to-lug keeps the 44.4mm case wearable
- Luminous hands and markers for low light
- One of Casio's more premium watches
Worth knowing
- 44.4mm sits at the larger end
Casio G-SHOCK GBM-2100A-1A3ER Solar Green alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification |  GBM-2100A-1A3ER | RA-TX0202B10B | AT2372-50E |
|---|---|---|---|
| Price | £229 | £219 | £229 |
| Case size | 44.4mm | 42.8mm | 44mm |
| Water resistance | 200m | 200m | 100m |
| Movement | Solar | Solar | Solar |
| Strap | Rubber strap | Stainless steel bracelet | Stainless steel bracelet |
| This watch |
|
|
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?
No. It charges from light, and the cell behind that is designed to last a decade or more.
Quartz, automatic and solar comparedWhat size strap does it take?
16mm. Any strap of that width will fit, and on most modern watches quick-release bars make the swap a two-minute job with no tools.
Will it fit my wrist?
Lug-to-lug is 49.3mm, 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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