Different Divers Watches

Scuba divers use a variety of watchlike devices to keep track of the amount of time spent underwater. This is not just for convenience; it's imperative that a diver know how long she has been at a certain depth in order to avoid nitrogen narcosis or other problems.

  1. Dive Watches

    • The "old-school" divers, that is, those who learned to dive before the advent of dive computers, used water-resistant watches to keep track of their underwater time. Dive watches are not just ordinary watches, however. Several factors protect them from the underwater environment.

      Though many watches are labeled "water resistant," not all of these are suitable for scuba or free diving. According to the Federal Trade Commission, no watch can be labeled "waterproof," as none can be guaranteed to withstand flooding.

      Rubber gaskets and O-rings provide a seal that prevents water from seeping into the machinery of the watch. In addition, the case of a dive watch must be made of material that can withstand the increased atmospheric pressure at depth.

      The standard by which a watch can be judged to be a diver's watch as opposed to a simply water-resistant watch is called ISO 6425. This was set by the International Organization for Standardization.

    ISO Standards

    • In order for a watch to be labeled as a diver's watch, it must adhere to the following:

      - Pass a test of reliabilty underwater
      - Pass a condensation test
      - Have crowns and setting devices that have been proven to resist overpressure and external forces
      - Be proven to be watertight and resistant to overpressure by water
      - Be proven to be resistant to thermal shock

      In addition, the diver's watch must possess these features:

      - A rotating bezel or other time selecting device, so that elapsed time can be easily seen
      - Numbers that can easily be seen in the dark at a distance of 25 cm
      - An indication that the watch is running, visible even in total darkness (such as a glow-in-the-dark second hand)
      - Magnetic resistance
      - Shock resistance
      - Resistance to salt
      - Solidity of the strap or band, such that it's not susceptible to outside force
      - The presence of an "end of life" signal for the battery

    Depth Ratings for Dive Watches

    • The minimum depth rating for watches meeting ISO 6425 standards is 100 meters. These watches are for dives to depths not requiring helium gas.

      Some dive watches are rated to depths of 200 or 300 meters. These are also suitable for scuba diving, but, again, not rated for depths requiring helium gas. For those deeper depths, diver's watches rated for a depth greater than 300 meters exist.

    Dive Computers

    • Today, most divers use a dive computer, which often has the appearance of a watch but offers additional information.

      Dive computers are designed using specific algorithms that follow the same principles as dive tables. They calculate depth, time and dive profile, establishing a safe rate of ascent that will allow the diver to avoid the necessity for decompression stops.

      Dive computers usually display current depth, maximum depth, water temperature, the length of the dive so far and the no decompression limit (NDL). The NDL is the length of time a diver can stay at the current depth without owing a decompression obligation. If decompression is necessary, the diver must spend a specified amount of time at assigned depth to allow accumulated nitrogen in the body to off-gas. Most divers prefer to avoid deco stops, so knowledge of the NDL is important.

      Most dive computers log a specific number of dives in the memory, so the profiles and statistics of previous dives can be accessed. In addition, they calculate the amount of nitrogen accumulated in the body, allowing for the amount of time spent on the surface interval.

      Most dive computers have a "plan" mode as well, which provides information as to how long a diver can stay at depth on subsequent dives, given the nitrogen load she is already carrying. This is especially useful for repetitive dives made in the same day. Some dive computers additionally provide "no fly" times, alerting divers as to when it is safe to board an airplane following dives.

      Most computers also provide warnings when a diver's ascent rate gets too fast. A fast ascent increases the risk of nitrogen bubbles in the bloodstream, which cause decompression sickness, or "the bends."

      Some computers can be set to accommodate Enriched Air Nitrox mixes, which have a higher concentration of oxygen to nitrogen than regular air. While nitrox does reduce the nitrogen load, it also creates a risk of oxygen toxicity, so it's important that, if a diver is on nitrox, she sets her computer accordingly.

    Integrated-Air Computers

    • Integrated-air computers function the same as ordinary dive computers, with one important difference. A sensor sends a signal to the computer, letting the diver know how much air has been consumed. While this information is normally available via an analog pressure gauge, the integrated computer gives the diver more specific information and often sounds an alarm at specific air-consumption intervals.

    Bottom Timers

    • Bottom timers bridge the gap between a diver's watch and a dive computer. Most display dive time, depth and temperature, and they keep a limited log of dives. They do not operate based on the complicated algorithms of dive computers and, therefore, can't provide warnings as to when a diver is nearing a no-decompression limit, or is putting himself in danger of oxygen toxicity. Rather, bottom timers operate on the supposition that the diver is keeping track of such things herself.

    Dive Watches vs. Dive Computers

    • While dive computers have made it possible to more accurately gauge the nitrogen load carried by a diver, some people argue that they also allow divers to do more complex, risky dive profiles without an adequate understanding of the risks. By substituting the computer's algorithm for manual calculations using a dive table, a diver can avoid really planning his dive.

      Before dive computers came into common use, divers routinely used tables, and therefore generally dove what is known as a "square profile." A square profile assumes you are descending to a specific depth, staying there, and then returning to the surface, with suggested safety stops. Some consider this limiting and overly conservative, as divers rarely descend directly to their maximum depth and stay there for the entire dive. A dive computer constantly recalculates the nitrogen load based on actual depths.

      The solution for many is to plan the dive using tables, and to use the computer at depth to ensure that the plan is adhered to. This allows the diver to remain in control of the parameters of the dive, yet does not restrict him to a square profile.

      Many divers wear a dive watch or bottom timer as a backup, in case of computer failure.