Time runs left to right. Each slot starts free at 0. A test occupies a slot only from the moment it can start. It takes the slot that lets it start soonest, the lowest slot when those times match. The bar is the width of its name. Each group has its own colour. A batch does not overlap tests from any other group. sequentially makes each step wait for the step before it. concurrently only waits for a free slot. An indented line continues the group.