Brain CoralDive Computer Series

Why Dive a Computer? – Ascent Rate Addendum!

Divers in Egypt. © 2010 Mika Hiltunen. Used with permission.

I’m a gear-o-phile. Okay now that we got that out of the way…

Dive computers are a great addition to your dive system. When a diver on a limited budget asks me what they should purchase first, a dive computer is always high on the list (usually right below regulators – but every situation warrants some thought). I don’t sell diving computers, I don’t get commission when one a diver buys one but I’m passionate about getting divers into computers.

And here’s why…

I missed one… arguably the one thing that genuinely separates dive computers from gauges & tables…

This is a little embarrassing… I use a computer on every dive

  • I don’t dive EANx (Nitrox) on every dive
  • I don’t always do multiple dives
  • I don’t always need a multilevel profile
  • The world doesn’t end if I forget to log a dive


There is one function that dive computers perform that I use on every single dive… they display your ascent rate! How could I possibly have left that off my list?!

Apparently familiarity begets forgetfulness or I have taken that function for granted (probably owe my dive computer an apology).

Our dive computers perform continuous monitoring to give us more dive time; adjust for various gas mixtures; calculate dive plans; and provide ease of logging all of which have acceptable (if less desirable) alternatives – the ability to calculate and display our ascent rate is one thing that is very difficult to replicate with other gear.

Maintaining a consistent rate slower than 30Ft/Min can be challenging especially for new and inexperienced divers simply because they don’t have a solid frame of reference for what if looks/feels like to ascend at the right rate. And for more experienced divers it’s one thing to do a proper ascent on a line… now move to open water with no frame of reference.

Timer & Depth Gauge

While it’s possible to use a watch and your depth gauge to measure ascent rate; this is especially impractical for new SCUBA divers or divers carrying extra equipment such as cameras. This method requires the ability to hold up your inflator/deflator hose with your left hand and hold both your timer and depth gauge with your right while making sure you can see both with the limited visibility afforded by a mask.

‘Bubbling’ Your Ascent

If you read or heard that you can just make sure you don’t ascend faster than your bubbles… this is only partially correct. The smallest bubbles you can see (typically ‘champagne’ sized) will generally ascend slow enough for you to follow; however, there are variables that change the rate of ascent rate of bubbles. More importantly for me, keeping track of a 1mm sized bubble in the wide open ocean is just impractical especially when I’m counting on that little bubble to keep me safe.

Your dive computer doesn’t care about currents, water temperature, the gas mix in your tank (Air vs. EANx is not so big a deal since N2 & O2 molecules are close in size – Helium (He) messes up the bubble ascent rate method though… side bar) or anything else when it comes to ascent rate. It’s just the change in depth divided by the time it takes you to make that change.

So, extended dive time is a really great consequence of using a dive computer but looking at my own diving I have to admit the feature I use more than anything else on my computer is the ascent rate display!

The surface interval’s over… get out there and dive!

SKuba Steve

© 2013 Stephen Krausse. All rights reserved.

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