Posted by MHK on March 13, 2001 at 13:22:34:
In Reply to: Dive tables vs. computers: only a $ difference? posted by AADIVER on March 13, 2001 at 12:17:36:
Frank,
Dollars and cents are a small part of the issue.
In terms of being equal value at computing NDL limits, I've put out several posts in this respect but let me see if I can make it clearer.
The assumption[s] in the following example is that you haven't modified the conservation factor in your computer and that the computer and the table that you are comparing is using the Buhlman model.. If you did modify the conservation factor then the analysis would vary exponentially to the modification.. As would the results vary if you are comparing a Buhlman model -v- a RGBM model...
If you did a square profile for 90' for 24 minutes the computer and the tables would tell you the same thing ( ie; you are at the M-value) ( there maybe a minor time advantage on the computer to account for the descent but immaterial for purposes of discussion)
However, to the extent that you did a *planned* table dive and went to 90' and only stayed for 5 minutes and then ascended to 60', the *table* diver may not have the wherewithal to compensate for the multi-level profile and thus would ascend at 24 minutes, whereas a computer would *compute on the fly* and allow for the added BT's available at the shallower depths.
So what I think is getting lost, or maybe I'm not doing a good enough job explaining, is that the manner with which these NDL limits are computed ( ie; the algorithim that provides for the slope intercepts are exactly the same) the major difference is that the computer generated algorithm has the ability to *compute on the fly* and thus gives different information to the same algorithm..
All that is being done is the compution of linear equations to compute the slope intercept ( a.k.a. the M-value that a given tissue compartment can tolerate). The two absolutes are the Compartment Inert pressure group and the Ambient Pressure and the slope is the ambient pressure line..
The formulas under the Buhlman are as follows:
y = mx + b format
Pt.toi i.g. = ( P amb/b) + a
Pamb.toi = (Pti.g - a) * b
So in short, it is these calculations that are done once at the surface ( ie; looking at your tables) or your computers constantly performs them underwater every minute at the varying depths..
Hopefully that de-mystifies the Table -v- computer algorithim issue..
If not let me know and I'll follow up..
Later