Function worked_between 

pub fn worked_between(
    plan: &Plan,
    work: &WorkItem,
    started: DateTime<Utc>,
    now: DateTime<Utc>,
) -> Result<f64, ScheduleError>

Hours between two instants of a task’s work, such as its start and the clock reading: working hours of the task’s calendar when the plan has calendars, elapsed hours otherwise; zero when until precedes from.

Remaining forecasts measure started work with it, and calibration measures recorded work with it, so both count the same hours.