Partial pressure of oxygen at a depth in feet, and the deepest a mix can be used for a given PO2 limit.
The formula: Max depth = (limit/fraction - 1) x 33. Change any box and the full working updates. For study only, never for dive planning.
The IMCA ADS, BDS and LST papers ask this as a four-option question, with a calculator on screen. A free account gives you 15 practice questions for each exam, each with the worked answer and the document it comes from.