Busy = share of the range spent running recipes. Near capacity (busy 80%+) is a hint to build another; Often stalled (20%+ of the time it had a recipe but couldn't run) usually means power, inputs or full outputs, and another machine won't fix it. Per type, busy and stalled average every machine of that type and EU/t adds them up; Uneven load means some machines of the type are far busier than others, so share the work out before building more.