It is obvious that we need to know the bottom time (time we have spent underwater) in our dives (read: dive computer). An underwater timer can be anything that has the ability to count and of course, should be waterproof.
This can be your everyday watch (if it is really waterproof) or any waterproof chronometer.
An analog dive watch has a ring on it (surrounding the watch). This ring start to turn clock-wise when you start to dive. You can also see the current time by the help of an analog dive watch.
Digital dive watch will display time passed from the start of the dive and the time that you have started to dive. It will also display the surface intervals (time spent between two dives on the land/surface).
Underwater chronometers will be activated when the pressure increases with the diver’s descend in the water and stops automatically when the diver surfaces.
I advise you to purchase a dive computer instead of a dive watch/chronometer. Majority of the divers who prefer to buy these equipment instead of a dive computer make their decision as a result of the price difference. Dive computers are more expensive than a dive watch.
However, I advise you to approach from this point of view:
Cressi Leonardo Scuba Diving Wrist Computer, one of the base models in the sector has a price of $249.95 & FREE Shipping in Amazon.com (by the time I am writing this article). It is a base model, with no transmitter and etc, but still does more than a dive watch does.
On the other hand, you can find a Casio Men’s MRW200H-7EV Sport Resin Dive Watch for $17.47 FREE Shipping on orders over $35. Let’s assume that you are going to pay 5$ for shipping instead of buying something else for around 18$ to benefit from the free shipping.
The price difference is $227.48 ($249.95 dive computer – $22.47 dive watch + estimated shipping)
As an instructor, I use my Mares Nemo Sport dive computer for more than 7 years. It seems I will use for another 3 years before I buy a new one. Even it will not be because this dive computer will last, but maybe will need a new look.
A typical diver with 30 dives per year will even use it more than 10 years when looked-after properly.
So, we are assuming that we will use our dive computer for 10 years (in fact it will be more). The price difference was $227.48. Let’s find the extra money we will pay for a dive computer instead of a dive watch annually.
$227.48 / 10 = $22.75
For $22.75/year, you’ll have extra features like alarm when the ascent rate violated, dive log, dive algorithm, dive planning and such. You’ll not need to check you depth gauge every time you need to check the depth. It’s gonna be a “all in one” situation for you.