M-Value — What It Is and Why It Matters
An M-value (Maximum Value) is the maximum tissue gas tension that a decompression algorithm allows in a specific tissue compartment at a given ambient pressure. It represents the theoretical threshold above which decompression sickness becomes significantly more likely. Each of Bühlmann's 16 tissue compartments has its own M-value line that varies with depth.
Gradient factors work by restricting divers to a percentage of the full M-value. At GF 80, for example, the computer limits you to 80% of the theoretical maximum tissue tension, adding a 20% safety buffer. The M-values themselves were derived from decades of research and empirical data on human decompression outcomes.
Learn More
Frequently Asked Questions
What happens if I exceed an M-value?
Theoretically, exceeding an M-value means your tissue tension is above the calculated safe limit, and the risk of bubble formation and DCS increases significantly. In practice, some divers have exceeded M-values without incident due to individual variability, but it is never a risk worth taking deliberately.
Are M-values the same across all algorithms?
No. M-values are specific to the Bühlmann model. RGBM and VPM use different constructs — RGBM uses bubble growth parameters and VPM uses critical bubble radius calculations. The concept of a maximum safe tissue tension exists in all models but is expressed differently.
Affiliate Disclosure: DiveComputers is a participant in the Amazon Services LLC Associates Program and eBay Partner Network. Links on this page may earn us a commission at no extra cost to you.