Periodic weighted avarage

It is the cumulative weighted average (and FIFO and LIFO) that is much more important for the exam (and in real life) and these are of course all explained in full in the free lectures.

Periodic weighted average, is simply adding up the total costs during the period and dividing by the total units purchased during the period, to get the average cost per unit.

(I do assume that you are not using the lecture notes on their own, but that you are also watching the lectures that go with them. If you are not watching the lectures for any reason then you need to buy a Study Text from one of the ACCA approved publishers and study from there.)