02 · Altitude
Altitude is the room you have left.
It is the distance between where work will land and where it must land, measured in working days. Positive altitude absorbs drag. Zero altitude means any drag causes a miss.
Altitude=Gravity date−Glide date
Pushing gravity down
Two passes give every task two dates.
Gravity is set on initiatives and epics, but altitude has to be known for every task. A forward pass from today finds each task's glide: the earliest it will finish. A backward pass from the commitment finds each task's gravity: the latest it may finish without moving the deadline.
- Each task under an epic inherits the epic's gravity date as its latest finish.
- Walking backward through dependencies, a task's gravity is the earliest gravity of anything that depends on it, minus that successor's duration.
- Each task now has a glide date and a gravity date. The difference is its altitude.
The critical path
The chain with the least room.
The critical path is the chain of tasks with the lowest altitude. Any drag on those tasks moves the commitment date. In the example, A, B, D and E each have three days. Task C has six and task F has eight, so a slip there can be absorbed.
Altitude is recalculated whenever glide changes, so the critical path is always current. When a delay shifts it, the model shows the new path immediately instead of waiting for someone to notice.
Runway
Room is relative to time left.
Runway is the time remaining before gravity. Five days of altitude is comfortable with a week to go and thin with six months to go, so the orbit states use the altitude ratio.
Ratio=Altitude÷Runway
Altimeter
Work out an item's altitude.
Enter today, the glide date and the gravity date. Weekends are skipped; holidays are not.