On-chain actions per ZEC in each pool per day. Caveat: action counting differs by pool type. Transparent counts inputs+outputs (2 actions per simple transfer).
Sapling counts spends+outputs (also 2 per transfer). Orchard counts actions (1 per spend-output pair). JoinSplits count as 1 each. This means Orchard appears ~half as active as Sapling/transparent for equivalent usage. Cross-pool comparisons are directionally useful but not perfectly apples-to-apples.
On-chain actions per ZEC held, per pool, per day — how hard each pool's value is working. High means the coins there are moving; low means they are sitting.
An “action” is not the same unit in every pool. Transparent counts inputs plus outputs, so a simple transfer is two. Sapling counts spends plus outputs, also two. Orchard counts actions, where one action is a spend-output pair — so the same payment scores one. Orchard therefore reads about half as active as Sapling or transparent for identical usage, and that gap is an artefact of the protocol's accounting, not a behavioural difference.
So compare a pool against its own history, where the unit is constant, and treat cross-pool differences as directional at best. The comparison this chart is actually good at is a single pool waking up or going quiet.