The Mudmaster adds a compass, pressure-based altitude information, temperature readings and step counting. It also adds 7.6 mm of thickness over the GA-2100. That is the trade to understand before getting lost in the list of modes.
Both watches offer the G-Shock format with analogue hands, digital information and 200 m water resistance. The black GA-2100 is the simpler everyday choice. The green-strapped GG-B100 makes sense when you want its instruments or deliberately prefer the much larger design.
The references compared
| Feature | Mudmaster GG-B100-1A3ER | GA-2100-1AER |
|---|---|---|
| Case length × width | 55.4 × 51.3 mm | 48.5 × 45.4 mm |
| Thickness | 19.4 mm | 11.8 mm |
| Weight | 92 g | 51 g |
| Power | CR2025 battery; nominal 2 years | Two SR726W cells; nominal 3 years |
| Solar charging | No | No |
| Bluetooth | Yes | No |
| Sensors | Compass, pressure/altitude, temperature, steps | No equivalent sensor package |
| Water resistance | 200 m | 200 m |
| Crystal | Spherical mineral | Mineral |
Specifications: Casio UK GG-B100-1A3ER specifications; Casio UK GA-2100-1AER.
Two different G-Shock directions from 2019
Casio dates the Mudmaster family to 2015, with the GG-B100 joining its 2019 carbon-construction programme. Four sensors and phone communication expanded the outdoor role alongside the protective case structure. Its battery-powered identity remains distinct from other Mudmaster references with different power systems.
The GA-2100 also arrived in 2019, combining an octagonal outline with a comparatively thin analogue-digital case. Later GA-B2100 models added solar charging and Bluetooth, but those functions do not belong to the basic GA-2100 compared here. The shared year therefore produced two very different answers: one expanded the watch’s equipment, while the other made the essential G-Shock idea easier to accommodate in daily clothing.
The dimensions should be the first decision
The GG-B100 measures 55.4 mm long, 51.3 mm wide and 19.4 mm thick. The GA-2100 measures 48.5 by 45.4 by 11.8 mm. The Mudmaster is larger in every published case dimension.
Its 92 g weight is still modest compared with many steel watches, but the GA-2100 is only 51 g. The 41 g difference is substantial within this pairing. Light materials do not make the bigger watch physically small.
Try the Mudmaster with a jacket cuff and while bending your hand. If the shape gets in the way of your routine, decide whether its functions are useful enough to justify the compromise. The GA-2100 removes a great deal of that bulk before any mode is switched on.
Buy the sensors for things you will use
The Mudmaster’s compass, step count and pressure information can add interest to ordinary walks. You do not need an expedition to enjoy them. The stronger buying argument is having a few repeatable uses instead of admiring the equipment list once.
The module 5594 instructions explain how to calibrate the pressure-based altimeter. Weather can change air pressure as well as elevation, so a known local height is a useful reference. Temperature readings also need to be interpreted with body heat in mind.
The GA-2100 gives up that sensor package. If your main requirement is local time, alarms and occasional timing, the omission can simplify the watch without removing the functions you actually need.
The phone performs part of the Mudmaster’s work
The GG-B100 includes Bluetooth through CASIO WATCHES. Its Mission Log combines watch altitude measurements with route information from your smartphone’s GPS. It is not a standalone satellite route recorder.
That division can be sensible when you already carry a phone. It becomes a limitation if your purpose is to leave the phone behind and record an independent route from the watch.
The GA-2100 has no Bluetooth. You use its own controls for settings. Someone who wants fewer device relationships may see that as part of its appeal, rather than a missing feature awaiting an upgrade.
Neither of these references is solar
The Mudmaster uses a CR2025 battery with approximately two years of nominal life. The GA-2100 uses two SR726W cells with approximately three years. Actual use of lighting, sensors and connections influences battery demands.
Neither recharges through light. Solar-capable G-Shocks elsewhere in the catalogue should not lend their specification to these exact references. If solar is a priority, it is a reason to compare a different model.
Both publish 200 m water resistance and use mineral glass, with a spherical crystal on the Mudmaster. The larger watch’s additional cost and bulk therefore do not buy a higher stated depth rating in this comparison.
The right amount of equipment
Choose the GG-B100 when its compass, altitude records, step display and phone-linked features are part of the enjoyment. Its layered black case and green strap can also be a deliberate aesthetic preference, provided you accept the dimensions.
Choose the GA-2100 when you want a lighter, much thinner analogue-digital G-Shock for a normal day. It covers the basic brief with less physical and operational complexity.
A watch does not need to be used at the limit of its specification to be worthwhile. It does need to suit the owner. The best choice is the one whose equipment adds interest or usefulness without making the case a recurring obstacle.
Based on manufacturer information. Specifications checked on 8 September 2026.
Image: AI-generated editorial illustration of the G-Shock GG-B100-1A3ER. Design details are approximate; this is not a product photograph.
