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==Gradient factors (GF)==
User input of [[gradient factor]]s is sometimes available for planning and real time applications.
Gradient factors are a calculation trick consisting in taking a percentage of each M-Value (e.g. 90%) in order to increase conservatism (shorter duration without mandatory stops, longer and/or deeper stops).
It is generally possible to define two GFs: GFlow and GFhigh. GFlow applies to the first (deepest) stop, GFhigh to the last stop (closest to the surface). Any intermediate GFs (between GFlow and GFhigh) are calculated by linear interpolation.
For dives without mandatory stops, only GFhigh is used, even if a GFlow is defined.
Twin GFs (e.g. 80/80) have the effect of artificially increasing dive time (time taken into account is greater than actual time). Using printed
==Tables==
Max Hahn first used Bühlmann's algorithm to develop dive tables for the Swiss Underwater Sport Association. In 1987, the [[Sub-Aqua Association|SAA]] Bühlmann System was developed by Bob Cole. This system used the dive tables and a set of rules so that people could dive safely and stay below their [[No Decompression Limit|no-decompression limit]].<ref name="Powell2008-18" /> The tables are still used today and are very popular; many dive computers still use the ZHL-8 algorithm and many tables are based on the ZHL-16 algorithm or derivatives. These calculations also include considerations for repetitive and [[altitude diving]].<ref name="AAB1984" /><ref name="AAB1987" /><ref name="Boni1976" /><ref name="AAB1973" /><ref name="AAB1989" /><ref name="AAB1984b" />
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