Cocobean and Danny,
when a diver is down below, then a dive watch/computer is the primary timing/safety device; if diving with a computer, then the watch is a secondary or backup timing device.
planning is crucial for each and every dive,
says, a planned dive profile allow the diver to dive at a certain max depth for 30 minute,upon diving into the water,he can use the bezel to time the dive,adjust the bottom time 30 minute a head of the minute hand.By looking at the watch and refering to the depth gauge he will know when to ascent to the surface this is crucial because the ascending time and speed will help to prevent decompression sickness.
A dive computer is a better choise because you can preset everything before the dive.
The tritium gas tube is better because it's clearer, brighter and it lasts longer!
Visibility during dives vary.It's not only occurs between different dive sites. Even at one site visibility may vary over a fairly short period of days.basically it's due to the current and weather.
The tritium gas tube will defintely outperform the conventional luminescent marker in a night dive!