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Casio Carbon Core Octagon Series 48.5mm X 45.5mm Mens Watch
Ref. GA-2100-1AER
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Stepping up in the same dial colour
The GA-2100-1AER wears its octagonal shape quietly, with a slim profile at 11.8mm thick and a resin case built around a carbon core guard structure for shock resistance. The black dial sits behind mineral glass, with analogue hands that shift aside automatically to clear the way for the digital display beneath. Functions include world time across 31 time zones, five daily alarms, a 1/100-second stopwatch with split timing, and a 24-hour countdown timer. A double LED provides adjustable backlight duration. The resin strap fits wrists from 145 to 215mm, and water resistance is rated to 200 metres.
- Reference
- GA-2100-1AER
- Brand
- Casio
- Collection
- G-Shock
- Case size
- 48.5mm
- Case thickness
- 11.8mm
- Case material
- Resin
- Dial
- Black
- Crystal
- Mineral
- Movement
- Quartz
- Functions
- Stopwatch, Countdown timer, Alarm, Backlight, World time, Perpetual calendar, Dual display, Digital display
- Water resistance
- 200m
- Bracelet / strap
- Rubber strap
- Strap colour
- Black
- Retailer
- F.Hinds
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 (85), Back in Stock (2,812), Watches 44mm and Over (711), Sports Watches (698), Watches Under £100 (502), Dive Watches (491) and All Black Watches (279).
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
- Second time zone for travelling
- Sits in the lower half of Casio's range as we list it
Worth knowing
- 48.5mm is a large watch with real presence
Casio Carbon Core Octagon Series alternatives
Watches from other brands at a similar price, style and size, so you can see what else your budget can buy.
| Specification |  GA-2100-1AER | RW647AX9 | RYS07-4004-SET |
|---|---|---|---|
| Price | £100 | £99 | £100 |
| Case size | 48.5mm | 46mm | 46mm |
| Water resistance | 200m | 100m | — |
| Movement | Quartz | Quartz | Quartz |
| Strap | Rubber strap | Stainless steel bracelet | Mesh 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?
Yes. It is quartz, so expect a battery change every two to three years at a jeweller.
Quartz, automatic and solar comparedIs 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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