Running order across groups

By default, each den runs its own round as a block: the Lions race straight through their round, then the Tigers race theirs, and so on. Between blocks somebody calls the next den forward, families move, cars are handed over — and the track sits empty while that happens.

Interleave heats across every den, a race setting off by default, fixes that by weaving every den's heats into one running order instead of one block per den — heat 1 might be a Lion heat, heat 2 a Tiger heat, heat 3 a Lion heat again — so the next den's cars are already staged while the current den races.

Turning it on

Tick Interleave heats across every den on the race form. It is not offered while creating a race — there is nothing yet to interleave — so create the race first and turn it on afterwards from the Event section of the race's edit form, under the track. See Race and track settings.

Turning it on renumbers nothing by itself — clicking Apply master order, below, is what weaves the heats together. What it does switch straight away is how race day runs: the Race tab, the Schedule tab's Run buttons and the audience displays all start following the running order rather than one round's block at a time. See Race day under the running order.

Applying it

Build your rounds exactly as you would for any other race — one round per den, raced however you like: every lane for everyone, Balanced, or Elimination. See Round styles.

Once the setting is on, a Master running order panel appears on the Schedule tab, above the ordinary per-round tables, listing every heat once in running order with the den it belongs to. Click Apply master order to weave the dens' current heats together into that order.

Heats already run keep the heat number they were called by. Applying the order never touches a heat that already holds a result — an announcer who has already called heat 6 will still find it as heat 6.
It is a deliberate, repeatable action, not a one-time setup step. Press it again any time — after adding a round by hand, say — and it recomputes the order from scratch over whatever heats are still pending. A round added or regenerated after the last apply numbers its own heats from 1 again, so re-apply once the schedule settles to weave it in properly.

Race day under the running order

While the setting is on:

The Race tab follows the woven order. After each heat, the next heat offered is the next one in the running order — usually another den's — and the On Deck panel shows that heat's line-up so the right cars are staged. The audience displays' Now Racing and On Deck follow the same order, so the wall always agrees with the operator's screen.
Any pending heat can be run from the Schedule tab. Rounds progress side by side, so Run is no longer greyed out on a round that is waiting for an earlier one to finish.
Dragging heats within a round is switched off, and the drag handle says so. A hand-reorder renumbers the round from 1, which would silently pull it to the front of the running order. Turn the setting off if you need to hand-reorder, then re-apply the master order.
A championship round still runs last. Its field is drawn from the dens' standings, so it is never woven in between them — it runs in its own order after every den's round is finished, exactly as it would without this setting.

What it does and does not change

Not a new way of scheduling. Every heat in the running order is a heat its own round already produced. A den's schedule — its matchups, its lane balance — is exactly what Round styles says it would be without this setting. All that changes is the order the heats run in.
Not a change to scoring. Each den's standings are still worked out from that den's own heats. Interleaving never averages one den's times against another's — see Scoring.
Not a merged round. The rounds stay separate. Advancement, when a round counts as finished, and the round-complete summary all work exactly as they do without this setting.

Two rules the order tries to follow

Every den finishes at roughly the same time. A den of four and a den of twelve, interleaved turn for turn, would run through the four-car den in the first quarter of the schedule and leave the rest of the event to the twelve-car den alone — the same "one den waits on another" problem this setting exists to fix, just moved later. Instead, each den's share of the running order tracks its own size the whole way through.
The same car is not staged twice in a row where it can be avoided. The point of interleaving is giving the crew that just ran a moment before their next heat, not sending them straight back to the line. This is best-effort, not a guarantee: if only one den still has heats left, there is nothing to weave it against, and a den's own schedule can already put the same car in back-to-back heats on its own (round styles do not promise otherwise). The running order never reorders heats within a den to fix that — it only decides which den's heat comes next.

Repairing the order as the day changes

A late arrival or a dead lane can add heats to a den mid-event — see Changes in the middle of a race. On a race with interleaving turned on, those new heats are woven into the running order automatically, right after the change that created them:

New heats are added after everything already numbered, never inserted in the middle. Nothing already on the board — run or still pending — ever gets a new heat number, so a heat you have already armed on the timer is never swapped out from under you.
Only the new heats are repaired. This does not recompute the whole running order the way clicking Apply master order yourself does, so it never disturbs a heat the announcer has already called.
Two dens that each gain heats from the same change — two latecomers checked in together, say — have their new heats woven together the same way the initial running order is, so they still finish at about the same time as each other.