PADI tables vs TDI/USN tables vs Dive Computer

[rhwestfall]

NAUI made one too (Dive Time Calculator II - did not do not ML). It was fantastic for my dyslexic daughter as the math gave her challenges in her early years.... she aced the tables portion of her exam with it.

 

[boulderjohn]

It was never exactly clear exactly where the arrow was pointing, is was not discrete, and gave ambiguous results.

When I took my instructor exam, when I did the work for a question using the wheel, I came up with an answer exactly in between 2 of the multiple choices. I did it again and again and again. I finally took a guess on one of the two and, of course, picked the wrong one. As required, the examiner went over my error with me, showing me with his wheel how to get to the correct answer. It worked. I then handed him my wheel and asked him to do it again. He got my wrong answer. That tiny difference in our wheels made all the difference.

Of course, the correct answer was "It just doesn't matter." In the real world, either answer was plenty close enough.

 

[Doc]

** The Wheel was a circular slide rule: an analog device. It was never exactly clear exactly where the arrow was pointing, is was not discrete, and gave ambiguous results.

It was adapted from an aviation widget that came from other slide-rule like adaptations.

@tursiops you really made me chuckle.

With the Wheel, to ascertain that it was printed and assembled in correct alignment, there was on the parts a set of dots that had to be aligned when in a specific position. It was an end-user quality check to make certain it was ready for use after purchase.

I was doing my OWSI final exam and we were doing the Wheel module. I worked the question but the numbers I came up with were not provided as possible answers, A, B, C, or D.

I checked the alignment dots. All good. Perfectly assembled and accurate. But still, my answer did not appear in the available choices.

I waddle up to the PADI Minor God who was the proctor. “I can’t work it for you”. I get that, but here, you try it. He took my Wheel, he worked it, then checked the alignment, then worked it again. As he dropped the Wheel in his briefcase, he looked up and said, “C”.

A very bizarre, likely un-relatable to most, but very telling in the checkered history of the teaching of multi level diving computations.

And then came the ERDP. I had a custom made housing made for mine!

 

[boulderjohn]

It was adapted from an aviation widget that came from other slide-rule like adaptations.

@tursiops you really made me chuckle.

With the Wheel, to ascertain that it was printed and assembled in correct alignment, there was on the parts a set of dots that had to be aligned when in a specific position. It was an end-user quality check to make certain it was ready for use after purchase.

I was doing my OWSI final exam and we were doing the Wheel module. I worked the question but the numbers I came up with were not provided as possible answers, A, B, C, or D.

I checked the alignment dots. All good. Perfectly assembled and accurate. But still, my answer did not appear in the available choices.

I waddle up to the PADI Minor God who was the proctor. “I can’t work it for you”. I get that, but here, you try it. He took my Wheel, he worked it, then checked the alignment, then worked it again. As he dropped the Wheel in his briefcase, he looked up and said, “C”.

A very bizarre, likely un-relatable to most, but very telling in the checkered history of the teaching of multi level diving computations.

And then came the ERDP. I had a custom made housing made for mine!

Ha! Probably the same question as mine in the post above yours. Yes, my wheel was perfectly aligned as well.

 

[shurite7]

@shurite7 , I’m just trying and hoping to flesh out your comment. It speaks to the history of the evolution of our understanding, and it also explains the hardware, from paper tables, plastic cards, wheels, and the dive computer.

No problem. The wheel was a great tool. It just came out late or one can say computers came out early and took it over. What the wheel did for me was help understand how to plan the dive, visualize what was happening in terms of NDL, and adhering to a plan. It also helped to understand what a dive computer is doing.

The big advantage the wheel still has over a dive computer is one can plan a multi-level dive and see the numbers, something a dive computer can’t do, in plan mode that is. This pertains to recreational diving, not tech.

 

[J-Vo]

Getting my engineering degree, no one ever told me it was impossible to understand calculus without a slide rule.

Why do people think you need one to understand decompression?

 

[Doc]

Getting my engineering degree, no one ever told me it was impossible to understand calculus without a slide rule.

Why do people think you need one to understand decompression?

Because I am not getting my engineering degree, Wolowitz.

 

[tursiops]

I have two Wheels (don't ask). An original and a Version 2.0 (Rev 5/2005). They differ in:

• Flying after Diving recommendations: (old) wait 12h, longer if multiple dives or days or deco dives; (new) wait 12h after single dive, 18h after multiple days or repetitive dives, longer than 18h if deco stops were involved
• Safety Stop guidance: (old) Safety Stops are required if the PG is within 3 Groups of a NDL limit, or if the dive is 100 ft or greater.; (new) Safety Stops are recommended (in same situations)

Note that the current versions of the RDP (table) say, re Safety Stops: required if (in same situations), i.e., like the old Wheel!

 

[tursiops]

Getting my engineering degree, no one ever told me it was impossible to understand calculus without a slide rule.

Terrible analogy! I can see what the point is you are trying to make, but you are not making it with this statement!

 

[boulderjohn]

Getting my engineering degree, no one ever told me it was impossible to understand calculus without a slide rule.

Why do people think you need one to understand decompression?

I think you are replying to shurite7's post, Josh, in which case you may have misunderstood it. He did not say he used the wheel to understand decompression; he used it to understand planning a multi-level dive. When planning a multi-level dive with the wheel, you planned 3 maximum depths, say 100 feet, 70 feet, and 50 feet. Then you figured out how long you could stay above each level and still stay within decompression limits. That is a type of planning that is rarely done on NDL dives. Yes, we do it on decompression dives using desktop software, but people don't do it on NDL dives.