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Instantaneous Gradient Factor for a tissue at ambient pressure P_amb:

Bühlmann M-value at P_amb: M(P_amb) = a + P_amb / b

Where:

• P_tissue — tissue inert-gas pressure (bar)
• P_amb — ambient pressure = 1 + depth/10 (bar)
• a, b — ZH-L16 Bühlmann coefficients for that tissue
• GF — 0 % at ambient (fully saturated, no gradient), 100 % at the M-value (Bühlmann limit)

During ascent the allowed GF is ramped linearly from GF Low at the pAnchor depth to GF High at the surface. The green corridor in the chart shows that allowed region.