What is spaced repetition?

The curve underneath it

The principle comes from Hermann Ebbinghaus and the forgetting curve: recall drops steeply in the first days after learning and then flattens, and repeated retrieval slows the decline. Spacing makes recall effortful rather than automatic; retrieval makes the person produce the answer rather than reread it. That is why a knowledge check is not decoration: being asked is the mechanism, not the measurement.

Count shifts, not days

Spaced repetition is usually described in days: review after one day, three days, a week. That assumes the learner is there every day. A person on a four-on, four-off pattern is not, nor is the weekend crew or the agency worker who is on your site for three assignments in two months. Set on a calendar, the second review lands on a rest day and the third after they have left.

The workable unit is shifts worked. A repetition on the second shift after the instruction, and again at the start of the next block, reaches the person while the task is in front of them. A review fixed to a weekday reaches whoever happens to be in that day.

What it is not

It does not replace the first instruction, and it has no legal status. Codex art. I.2-21 and Arbowet art. 8 set no refresher interval for general instruction; the Codex says training is repeated and adapted as risks evolve, and spacing is a method for meeting that. The few fixed intervals (first aid, VCA, Code 95) are in the guide on how often training must be repeated. The guide on training in shift-based operations places the intervals against a real roster.