[et_pb_section fb_built=”1″ _builder_version=”4.16″ _module_preset=”default” background_image=”https:\/\/punkfish-academy.com\/wp-content\/uploads\/2022\/03\/Rebi-1024×635.jpg” global_colors_info=”{}”][et_pb_row _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” text_orientation=”center” text_text_shadow_style=”preset5″ text_text_shadow_blur_strength=”1.7em” text_text_shadow_color=”#000000″ global_colors_info=”{}”]<\/p>\n
[\/et_pb_text][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_row _builder_version=”4.16″ _module_preset=”default” custom_margin=”|auto|-3px|auto||” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”]<\/p>\n
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In the last part, we learned about the M-values as “maximum tolerated supersaturation”. We also saw that these M values are not a hard limit, but represent an empirically estimated tolerable risk – and what we consider safe today may be different for some divers than it was half a century ago.
Saturating tissue up to the M value does not seem to be a good idea, and cases of DCS are already occurring at values below this. So how much distance do we want to keep from these values at what moment of the dive? This \u201csafety margin\u201d is what the gradient factors (GF) are all about<\/p>\n
Gradient factors are modifications of the B\u00fchlmann model that attempt to adapt the model to more recent findings and theories. They create a kind of “distance” to the M-values, but at the same time a clear modification: You change the model without having actually tested the consequences empirically. Therefore, a little caution is in order. In the area of gradient factors, the uncertainties are quite large, and in fact not all of these modifications may provide a real safety gain.<\/p>\n
[\/et_pb_text][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ _builder_version=”4.21.0″ _module_preset=”default” custom_margin=”||0px||false|false” custom_padding=”||0px|||” global_colors_info=”{}”][et_pb_row _builder_version=”4.27.4″ _module_preset=”default” background_color=”rgba(132,157,183,0.83)” border_radii=”on|20px|20px|20px|20px” border_width_all=”2px” border_color_all=”#FFFFFF” box_shadow_style=”preset6″ box_shadow_blur=”37px” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”]<\/p>\n
[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”3px|||||” global_colors_info=”{}”]<\/p>\n
[\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”1_3,2_3″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”1_3″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”]<\/p>\n
<\/a>We have learned about this graph with the M-line in the chapter about M-values. When you surface to this limit, the tissue reaches a supersaturation equal to its M value.<\/p>\n If you don’t go as far as this line, but stop before it, you maintain a kind of “safety distance” from this perhaps too risky limit. You can draw such a line with the gradient factors: You shift the M-line downwards – or you even bend it a little. [\/et_pb_text][\/et_pb_column][et_pb_column type=”2_3″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_image src=”https:\/\/punkfish-academy.com\/wp-content\/uploads\/2025\/03\/M-Linien-mit-GF.png” alt=”Gradients and M-values” title_text=”M Lines with GF” show_in_lightbox=”on” _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”][\/et_pb_image][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”||0px|||” global_colors_info=”{}”]<\/p>\n So far, so simple. Usually, however, the gradient factors are specified as a pair in which the first number is smaller than the second. “GF60\/80”, for example, or “GF30\/70”, or whatever combination. When do I want to stop for the first time during the ascent, and consequently what inert gas overpressure of the tissues (leading at that time) can I tolerate at depth? And with what safety distance do I want to reach the surface?<\/p>\n These distances are defined by the Gradient Factor Low (GF Low) and the Gradient Factor High (GF High).<\/p>\n The GF Low determines the maximum accepted inert gas overpressure in the tissue when the first stop is reached, while the GF High determines the maximum accepted inert gas overpressure in the tissue when the surface is reached. If different values are used here, the result is not simply a shifted line, but a curve towards the higher value. <\/p>\n [\/et_pb_text][et_pb_button button_text=”Choosing Gradient Factors” _builder_version=”4.27.6″ _module_preset=”1b468ece-fbc6-41f0-9fbb-0d9bc6882bdc” button_url=”@ET-DC@eyJkeW5hbWljIjp0cnVlLCJjb250ZW50IjoicG9zdF9saW5rX3VybF9wb3N0Iiwic2V0dGluZ3MiOnsicG9zdF9pZCI6Ijc2NzUiLCJlbmFibGVfaHRtbCI6Im9mZiJ9fQ==@” _dynamic_attributes=”button_url” hover_enabled=”0″ sticky_enabled=”0″][\/et_pb_button][\/et_pb_column][\/et_pb_row][\/et_pb_section][et_pb_section fb_built=”1″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_row _builder_version=”4.27.6″ _module_preset=”default” background_color=”rgba(174,193,242,0.83)” hover_enabled=”0″ border_radii=”on|20px|20px|20px|20px” border_width_all=”2px” border_color_all=”#FFFFFF” box_shadow_style=”preset6″ box_shadow_blur=”37px” global_colors_info=”{}” sticky_enabled=”0″][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”]<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.16″ _module_preset=”default” custom_margin=”|auto|-3px|auto||” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” custom_padding=”0px|||||” global_colors_info=”{}”]<\/p>\n [\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row _builder_version=”4.21.0″ _module_preset=”default” custom_padding=”4px|||||” global_colors_info=”{}”][et_pb_column type=”4_4″ _builder_version=”4.16″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.27.6″ _module_preset=”default” hover_enabled=”0″ global_colors_info=”{}” sticky_enabled=”0″]<\/p>\n If you want to keep track of which tissues are saturating or desaturating at any point during the dive, and how close they are to the limits, you can see this in a very simple format: the heatmaps used by Subsurface<\/a>. You can easily download this planning and logbook tool; for analyzing dives, it is best used on a PC. [\/et_pb_text][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”3_5,2_5″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”3_5″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_text _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”]<\/p>\n Let’s take any dive. If we look very closely at the colored strip below, the heat map, it becomes clear that there are 16 differently colored lines superimposed here. These lines are the 16 tissues (compartments) of the B\u00fchlmann model: the fastest tissue at the top, the slowest tissue at the bottom.<\/p>\n All tissues saturate during the dive. This process is shown in different shades of blue, the lighter, the further the tissue is from saturation. Purple means almost complete saturation, black means complete saturation. This, of course, is always measured against the ambient pressure: if you go deeper, you move away from the state of saturation and then slowly saturate up, each tissue in a different time. During ascent, the current saturation state of the tissue turns into overpressure, and desaturation sets in.<\/p>\n The desaturation is displayed in traffic light colors: Green means that the maximum permitted value – the M value – is still very far away, yellow brings it closer, in the orange range you get to a GF of 60-60, and red stands for the M value. If the heatmap turns white, this limit has been exceeded.<\/p>\n You can now see exactly which tissues are affected at which point in time during the dive – all tissues at once, a possibility that no other display format offers so easily.<\/p>\n [\/et_pb_text][\/et_pb_column][et_pb_column type=”2_5″ _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][et_pb_image src=”https:\/\/punkfish-academy.com\/wp-content\/uploads\/2023\/09\/20-min-30m.jpg” alt=”Dive profile 20 minutes at 30m” title_text=”20 min 30m” _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][\/et_pb_image][et_pb_image src=”https:\/\/punkfish-academy.com\/wp-content\/uploads\/2023\/09\/Subsurface-Heatmap.jpg” alt=”Subsurface Heatmap Legend” title_text=”Subsurface Heatmap Legend” _builder_version=”4.21.0″ _module_preset=”default” global_colors_info=”{}”][\/et_pb_image][\/et_pb_column][\/et_pb_row][et_pb_row column_structure=”1_3,1_3,1_3″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_column type=”1_3″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_button button_url=”@ET-DC@eyJkeW5hbWljIjp0cnVlLCJjb250ZW50IjoicG9zdF9saW5rX3VybF9wYWdlIiwic2V0dGluZ3MiOnsicG9zdF9pZCI6IjMzNDYiLCJlbmFibGVfaHRtbCI6Im9mZiJ9fQ==@” button_text=”Saturation and desaturation” _builder_version=”4.27.4″ _dynamic_attributes=”button_url” _module_preset=”default” global_colors_info=”{}”][\/et_pb_button][\/et_pb_column][et_pb_column type=”1_3″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”][\/et_pb_column][et_pb_column type=”1_3″ _builder_version=”4.27.4″ _module_preset=”default” global_colors_info=”{}”][et_pb_button button_url=”@ET-DC@eyJkeW5hbWljIjp0cnVlLCJjb250ZW50IjoicG9zdF9saW5rX3VybF9wYWdlIiwic2V0dGluZ3MiOnsicG9zdF9pZCI6IjEzODYzIiwiZW5hYmxlX2h0bWwiOiJvZmYifX0=@” button_text=”Foll Course” _builder_version=”4.27.6″ _dynamic_attributes=”button_url” _module_preset=”1b468ece-fbc6-41f0-9fbb-0d9bc6882bdc” global_colors_info=”{}”][\/et_pb_button][\/et_pb_column][\/et_pb_row][\/et_pb_section]<\/p>\n","protected":false},"excerpt":{"rendered":" How can gradient factors modify the degree of supersaturation?<\/p>\n","protected":false},"author":1,"featured_media":7655,"parent":0,"menu_order":0,"comment_status":"closed","ping_status":"closed","template":"","meta":{"_et_pb_use_builder":"on","_et_pb_old_content":"","_et_gb_content_width":"","pmpro_default_level":"","footnotes":""},"class_list":["post-5207","page","type-page","status-publish","has-post-thumbnail","hentry","pmpro-has-access"],"yoast_head":"\n
How exactly? First of all, you look at the distance between the (current) ambient pressure and the M value and take a percentage of this. This then becomes the new M value. <\/p>\n
Two different points are set here during the ascent: <\/p>\nAll tissues in view at the same time<\/h2>\n
Representation of 16 tissues as a heat map<\/h3>\n
For a basic introduction to Subsurface, you can find a summary here: Planning dives with Subsurface<\/a><\/p>\n