Ascent rate indicator

[Scuba]

I have seen several posts which mention that there are better methods to gauge ascent rate than the computer's ascent rate indicator, due to the lag in response time.

The time it would take for the sensory information to be transmitted to the CPU, which will then process the calculations necessary and tranmit it to the display module, would be almost instant for practical purposes.

Unless:
the computer is very slow?
the sensor is not adequately responsive?

The problem I see is in the way this information is displayed. For example, my computer starts displaying ascents at 20 fpm and successively in 10 fpm increments up to 60 fpm. I have seen mention of computers displaying lesser increments. Are there any which display ascent rates using numerical digits?

Given the importance of ascent rates, with new research increasingly pointing towards slower ascents. I would consider an accurate ascent rate guage on of the most important pieces of information a diver needs.

I know the old pro's are going to metion how its just not necessary. I can drive my car anywhere without a speedometer, but it sure is nice to have one for a glance once in a while.

The ascent rate display is one case where technology is just not being properly utilized by divers. Unless there is some technical obstacle tha I am not aware of.

 

[nickjb]

I suspect the delay would be due to sample rates. As you say, sensing and processing would be fast.

My suunto has a bar graph with a block for 2/4/6/8 metres/min and an alarm at 10 metres/min ,I think (x3 for feet). When I am ascending (espcially above 10m) I try to keep the indicator clear, ie less than 2m/min.

I am trying to use static objects and 'stuff' in the water but it is nice to have guage

 

[Uncle Pug]

..with using the computer ascent function during ascents is that your situational awareness goes down the crapper.... and if the computer is what you are relying on then you have to watch it like hawk or your *lag* time will be reeeeally big. Forget this business about instantaneous measurement*computation*readout.... if you are scanning your environment and buddy like you should your ascent meter can't help you except by sounding the alarm... and then it's too late.

When watching the stuff in the water for reference (and occassionally glancing at the depth gauge to determine your actual as opposed to relative depth) you are also looking around you and are aware of your environment and your buddy.

Not so those who are glued to their computer.

If you don't develop this skill you won't have this skill and you can't develop this skill by looking at your computer.

You can blow this off... but what I am telling you is the truth of the matter.

 

[Scuba]

nickjb,

You're probably correct if in fact there is lag time. Can someone attest to this?

Increasing the sampling rate would be easy to accomplish. This is not a technical hurdle.

The problem I see is that the information is simply not adequately presented. To display increments of 6 ft., 2 m./ min. in your case, 10 ft/min in mine, might have been acceptable when the ascent rate was considered adequate at 60 ft/m.

Makes you wonder how far behind the curve some of the equipment manufacturers really are. Some are still designing for the old divers, who probably won't use one anyways.

There is a natural resistance to new technology. But computers are not new any more. When it comes to accuracy and reliability in gauges, I'll take a computer any day. Given they their equal in quality design and construction.

 

[Scuba]

Thank you Uncle Pug for bringing up the issue of situational awareness. I certainly value your opinion based on all the diving knowledge you share in your posts.

Nonetheless when we drive a car we are not glued to the speedometer, but it sure helps make driving safer by being able to glance it and verify our speed, allowing us to make accurate corrections as necessary.

 

[redacted]

It's not so much a computer limitation as a compromise between detecting real ascents and things that look like an ascent. If the computer was programmed to believe that a 1 ft ascent in a second was real, many of us would be sounding the alarm by just lifting our guage. The problem is only compounded by the accuracy of the change of depth measurement. So some type of buffering is necessary and desirable. With a high sampling rate, the smoothing algorithm would need to be fairly complex to avoid false alarms. With a lower sampling rate, little on no smoothing would be required but lags would be more apparent.

 

[Rick Murchison]

Current displays aren't worthless... just nearly so. *Anything* is better. Junk in the water, a down line, anchor line, bottom, wall, sweep second hand and depth gauge... anything. The displays are in desperate need of modification. To be useful they need at least ten times the increments they have now.
Rick

 

[MSilvia]

using an Ascent Rate Indicator is probably okay if it makes you more comfortable, but how well prepared are you to make a safe ascent from 80' if your computer craps out? Do you prefer it, or rely on it?

I learned ascent on environmental cues, and have used them ever since. My computer has an ascent gauge, but I consider it a novelty... I might glance at it out of curiosity. My ascent from depth rates are typically good when I look at the post dive summary. (except for one time when I was freaked out and task loaded, but an ARI wouldn't have helped that.)

The only time not using one has ever been a problem was when a buddy was suprised/alarmed that I wasn't using him (and his computer... I didn't have one at the time) as a reference. Frankly, it never occurred to me I might want that.

I'm with Uncle Pug... give me floaties over flashing beepers any day.

 

[Rockhound]

for recording and displaying information. I would really miss my computers if they were taken away from me.

But, they are not "predictive devices" and lack the necessary AI programming to project trends or provide advance warnings (although the deco features of them can be used in a predictive fashion, they only record past events and make calculations based on the "moment" and not on future possibilities. Suddenly go deeper and they recalculate your NDT or DECO. They don't give you advice like "don't do what you're thinking of doing, you idiot"....)

Even if they did contain high resolution predictive features, as someone aptly pointed out, "They would be alarming every time you raised your arm"--interpreting those transient actions as an ongoing action.

A fully aware, experienced diver controls his ascent rate by observing the water around him, sensing changes in pressure, sensing changes in water flow, watching small bubbles or fixed reference points and, sometimes, just by being intuitive. He can use his ascent indicator to supplement/confirm this information, but he cannot...SHOULD NOT focus on it as his primary source of information.

When you drive your car down the highway, you have your speedometer for information on your speed. But you mostly rely on that instrument, when using it properly, to give your confirmation of your speed. You don't need to fixate on the needle to know that you are increasing speed as you go down a long grade. You sense it and you react BEFORE the instrument indicate you are traveling too fast. By the time the needle says 90MPH, you are already (duh) doing 90. But, aware of the conditions, a good driver would have already sensed the acceleration BEFORE reaching an unsafe speed, and reacted accordingly.

The best pilots fly "by feel". relying on their instruments for backup and for when conditions really deteriorate or for confirmation of engine and flight performance (mixture, EGT's, etc.). They listen to the sounds of the engine, they "feel" for cues to performance and they use their eyes, their ears and their brains to fly smoothly and safely.

Yes, they need instruments, but they do NOT rely on them.

Some of the poorest pilots are "needle chasers", always reacting too late or overcompensating because they don't develop a "feel" for the aircraft, but instead, rely on the VSI or gyro or ASI to tell them what to do. But these instruments don't tell you what to do, they tell you what you DID. Better pilots, even when flying on "instruments" learn to "predict" trends and to filter out data that is inconsequential, transient, or "spiky". The data is there and VERY necessary when visual clues are missing and when equilibrium can't be trusted, but the ability to read the data is only part of it. The most important part of it is the ability to "interpret" the data and to use all your senses and intelligence to do so.

Ascent rate indicators on dive computers, to my knowledge, lack predictive (AI) algorithms. While models exist to predict trends and could be applied to these devices, such methods can't be trusted due the "smoothing" that must be done for arm motions, wave action and body repositioning. No matter how fast they react, by the time you see what you have done....well, heck, you've already DONE IT. They don't show you ascending too fast until such an action is part of the past. Bar (or needle) movements might give you some idea of trends, but the accuracy and detail they require to give you useful information might get lost in the "noise" of normal diving actions.

The best instruments we have for ascent control is the same ones we should rely on for all of our dive parameters: Our intelligence, our experience, and our intuition.

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