Mental Math Basics, what is your most useful tip?

[Cacia]

TSandsM recent "mini" thread on how tech divers approach deco without computers has made me think.

Many are not at that level...I know some of it is over my head. So, what are your simplest, easiest to remember ways of keeping track of your profiles?

Mine, is the "120 rule" Pug mentioned once. I realize it is not perfect on the "outside" , but it give me an easy way to check my interpretation of my computer.

120-depth= time

Anybody have some to share?

 

[TSandM]

Actually, if you go to the 5thD-X site (http://www.5thd-x.com/index2.html) and click on Learning Center, then go to PDF's and choose Dive Planning, and then run down to Battlefield Calculations, there are a whole ton of quick tricks for mental math.

A lot of the dive planning mini I did the two days before the Rec 2 class was going over these mental arithmetic things. They may seem difficult or obscure at first, but by the end of five days, we were all doing them more or less in our heads.

The GUE tables are easy, too. 100 feet -- 20 minutes. Down ten, five minutes less. Up ten, five minutes more. This works between 70 and 130. 60 is 50 minutes, 50 is 60, and 40 is 170. So you really have only four numbers to memorize. (Note that this is based on doing GUE's minimum deco, though.)

 

[Jon C]

Stay shallow & empty tank. So I guess the formula is:

(Starting PSI - Starting PSI + Time it takes to have my toes go numb = dive time).

As you know Catherine, the Laguna Beach sites are hard pressed to reach 50 feet. On boat dives I just rely on the computer for multiple dives and tend to stay relatively shallow (<120 feet) anyway. And (seriously now) I always end up on the anchor chain with 500 psi. The time it takes the crew to refill the tanks make for a solid deco period before the next dive.

Jon

Only 246 days 'til Maui...

 

[Cacia]

The GUE tables are easy, too. 100 feet -- 20 minutes. Down ten, five minutes less. Up ten, five minutes more. This works between 70 and 130. 60 is 50 minutes, 50 is 60, and 40 is 170. So you really have only four numbers to memorize. (Note that this is based on doing GUE's minimum deco, though.)
__________________

I think making it doable is a big plus!

Thanks for the site. I am practicing tracking my computer....checking it along the way, etc. Of course, it has arrested my shooting manual goal.....my boat docking goal...that is my story and I am sticking to it.

I think that is great that GUE is putting those sites up.

Is GUE minimum deco the half depth pause and the one minute at each ten foot increment before the twenty foot 3 minutes...or is it more complicated? How do you define "GUE mininum deco"?

What are the four numbers? time, depth...

(oh, so that's ratio deco?)

 

[JeffG]

I think that is great that GUE is putting those sites up.

It wasn't a GUE site. Its the Heretics site.

 

[TSandM]

Pause at 75% max depth (in rec range) rounded shallower to the nearest 10 feet. Hard stops of one minute start at 50% of max depth and continue to the surface.

So, 100 foot dive: Pauses at 70 and 60, a minute at 50 and each ten feet thereafter to the surface.

This is for dives within the MDL (minimum deco limits).

 

[Cacia]

oh...you should be teaching this stuff. Thanks.

I was confused about the 75%, 50 % pause/ minute part.

I think as the toolbox leaks out, the politics of DIR will fade. That only occurs when there is a vacume. Very useful stuff.

Also..."no plan survives the water" is more useful than the "plan your dive, dive your plan". Operating in the space between the two feels about right.

 

[rjack321]

When using 32% just lop off 20ft from your depth for 110,100,90 ft depths.

Subtract 10ft from your depth on shallower dives

e.g.
100ft on 32% = 80 on air
60 on 32% = 50 on air

 

[neil]

I was born severly math-impaired so I would have to write even the shortcuts on a slate. It's all I can do to remember my rock bottom number. I think it's 46.

 

[TSandM]

Remember, rock bottom depends on your depth and the tank you are using . . .