Method of detection of the beginning of a dive for a dive computer

The method involves comparing a value of variation in pressure between measured ambient and reference pressure values to a trigger threshold. A dive mode is activated if the variation value is higher than the threshold, and the value is compared to a preset quantity. The reference value is corrected if the variation value is higher than the quantity, and the last measured value is stored as a new reference pressure value. Independent claims are also included for the following: (A) a computer program comprising instructions to perform the dive detection method (B) a portable electronic device comprised of a controller circuit.