Master of G

The Master of G is a line of G-Shock watches produced by Japanese electronics company Casio designed for usage in harsh environments. Many showcase new technology that Casio would eventually introduce into the G-Shock and ProTrek line of watches, such as an altimeter, digital compass and the Tough Solar feature.
History.
The Master of G series began in 1985 with the G-Shock II DW-5500C. This was a classic square case G-Shock watch, but the bezel contained softer parts and slipped over the buttons. This way Casio created a Mud Resistant structure. The DW-5500C was therefore nicknamed "Mudman". 
In November 1993, Casio introduced the G-Shock Frogman model in Japan; the case-back featured the word "FROGMAN" and a small figure of a diving frog. It was made for divers; it featured a unique asymmetrical design of thick rubber shielding around a self-contained module. It came with a titanium screw-back case - an unusually high-cost design. It had a thick double-tang resin strap. A digital feature was dive timing. The Frogman proved to be very popular and at some point between then and 1995 Casio decided to produce more variations, including limited edition colours that in some cases have become very valuable.
The Master of G watches ceased production in 2000, but there were signs Casio was keen to keep the range alive, not just with limited edition releases but with re-designs of some of the old models.
In 2006, the new Mudman models were introduced in the Master of G range of watches followed by the new Gulfman models in 2007.
Subsequent new models have since followed which have more advanced features. The Rangeman series was introduced in 2013 and has ABC (Altimeter, Barometer, Compass) features, along with added GPS connectivity being introduced in 2018. The MASTER line was designed for land, aviation or sea related activities. The watches in the MASTER line include the Mudmaster (designed for people related for the army or people related with land related jobs), the Gravitymaster (designed for pilots or people related with aviation industry) and the Gulfmaster (designed for marine forces or people related with the shipping industry).
Characteristics.
Master of G series watches are invariably amongst the largest G-Shock designs Casio produces, usually suited for those with larger wrists. They are almost always named with a "man" suffix after the initial Frogman model which itself was named for scuba divers. Three models, the Mudman, Gaussman, Raysman and Rangeman all feature a thick rubber outer layer that surrounds the buttons and case completely, ensuring that they offer mud-resistance. The Gaussman was also ISO-certified anti-magnetic.
Most models consist of a steel case surrounded by a thick neoprene or polyurethane bezel and outer protection. All models except the earliest Frogmam models feature Casio's Illuminator display lighting system and are water resistant to 20 atmospheres (20bar/200metres) which thus makes them suitable for scuba-diving except at depths requiring helium-oxygen gas.
Some of the modules incorporate highly advanced functions. The Riseman features twin sensors that measure both temperature and atmospheric pressure, thus allowing it to serve as a barometer and altimeter. The Raysman was the first model to make use of Tough Solar technology to power its functions, the Wademan featured a digital compass, the Fisherman helped introduce the now-common tide graph and moonphase readouts, and the Antman was the first Casio watch that received an atomic signal that calibrated its timekeeping with atomic clock transponders in Japan.
Today, it is not unusual for two or more of these features to be found in a single Master of G model i.e. the GW-9200 Riseman has Tough Solar to power its radio-calibrated timekeeping and altimeter/barometer/thermometer functions; the GWF-1000 Frogman and GW-9110 Gulfman both feature solar power, radio timekeeping and tide and moon phase indicators. The current GW-9400 Rangeman with triple sensors has the most extensive feature sets so far, with mud/dust resistance, solar power, radio timekeeping, thermometer, barometer, altimeter, and digital compass functions, which have long been provided on Protrek/Pathfinder series. The GPR-B1000, which is the successor to the GW-9400, and is also named Rangeman, has advanced GPS functionality in addition to the triple sensor features of its predecessor.
Collectibility.
Earlier and rare models of the Master of G series command strong resale values; examples in NOS (New Old Stock) condition command a premium. Prices are sometimes higher outside Japan, not least because many models were produced only for the domestic market rather than for North America and Europe.
There have been several limited editions of the Masters series, and depending on their scarcity these command some of the highest prices for any of Casio watches. The "Men in Black" and "Men in Yellow" series are black and yellow versions of the Masters and typically command anywhere between two and three times the resale value of the regular versions. Some models such as the "Brazilian" Frogman and A.R.T.P.I Wademan are even scarcer and can command even higher prices, though their value is hard to predict as there are limited numbers and the price is largely determined by demand from individual collectors.
Although not always available, all models are usually valued at US$500 or less, providing an affordable alternative to the collecting of prestige watches.