Before buying a scuba dive computer ....?
What type of diving do I want to do?
Think about your current scuba diving and where you would like your scuba diving progress to, it doesn't have to be a plan, just something where you would like to be - especially in the next couple of years - Air diving, EANx (Nitrox), gas-switching, decompression, tri-mix, semi-closed, fully-closed rebreathers, wrist/watch/console style?
Do I want to log my scuba dives and post analyse the scuba dives?
Then you would require a scuba dive computer that has a download / PC interface.
Do I want to measure current gas consumption on my scuba dive and have information recalculate my remaining scuba dive time?
Then your scuba dive compute will need to be a fully integrated dive computer console, or have the ability to receive data from a transmitter.
Do I want to use my scuba dive computer as a watch outside of diving?
Then it will need to be a wrist-watch type scuba dive computer.
How much money do I want to spend on my scuba dive computer?
Set yourself a budget and see what is the best dive computer you can buy. If you can afford, after you made the selection, add another £50 / €50 and see what you can buy, what additional dive features do you get - it often adds more flexibility as your scuba diving progresses. The last thing you want, is having to replace your scuba dive computer when you do the next course. Your dive computer should give you years of scuba diving support.
Scuba Dive Computer - Case Study

Sunnto D9When I started out in scuba diving, I never thought I would become an scuba diving instructor or even a rebreather diver. Initially, I wanted to buy a cheap and cheerful Suunto Gekko, but the dive shop owner suggested going for the Suunto Vyper, allowing for Nitrox diving. Even though, I didn't do my Nitrox qualification for a number of years, I was very happy to have the ability to do the course without having to invest in another scuba dive computer.

A few years later, I decided to join a trip to Scapa Flow, one of the top dive sites in the world. However, a lot of the wrecks were deeper and I wanted to extend my bottom time. After completing another course, that allowed gas switching for accelerated decompression, I noticed my dive computer was not up for the task. Apart that it is recommended you wear two scuba dive computers, in case one fails. 

I decided to purchase a Suunto D9 scuba dive computer  - it allowed for three different gases, I could wear it on my wrist as a normal watch, the integrated digital compass works well (especially on holidays) and I could use the transmitter on it - allowing to monitor each of my two cylinders on the twin set (in case of a shut down). My trusty old Suunto Vyper - still around, in gauge mode for both the twin-set and the rebreather.

This means after 12 years of diving, I am still using a lot of the equipment I originally bought when I started out - there is a simple reason for that - I had usually spend initially more than I wanted - but had to spend less at the end. 

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