How many qualified people do you need on every shift?

Each holder is treated as absent on some share of their rostered shifts: 25 days of paid annual leave plus 8 days of average sickness across 261 working days, which is 12.6 percent. A binomial across the holders gives the chance that fewer than the required number are present on a given shift, and multiplying by the shifts in a year turns that into a count a planner can argue with. Where an operation runs fixed crews, the arithmetic is done per crew and added up, because a holder on another crew is not on this shift.

The model treats absences as independent and every certificate as valid, and both are generous. Holders who trained together take leave together, and a lapsed certificate removes a holder for the weeks a renewal takes. Every figure here is therefore a floor on the real exposure. The leave and sickness inputs vary by country; the relief factor library carries sourced figures for 17 of them.

These pages do not state any regulator's minimum. A regulation typically names the number that must be appointed or present; the arithmetic here answers the question that follows, which is how many must hold the qualification for that number to be there on the day. Read the one next to it on how many of the team can be off at once for the same distribution applied to the whole roster.