A studio-era invention with an accountant's soul: a grid of your cast against your shoot days: Start Work, Work, Hold, Finish. The row that matters is Hold: a performer paid without filming, and it's a real charge only on weekly and consecutive-employment deals, not on a local day player, who has no span to hold open. Studios built the DOOD to find those chargeable gaps and squeeze them out by reordering the schedule. It's still the fastest way to price a calendar: one glance shows whose time you're wasting. I rebuild yours live as strips move, so the expensive holds surface before they're spent.