A means to simply distribute upcoming work evenly (heijunka). Literally a box of slots or "cubbyholes" arranged in rows by part number or part type and in columns by identical time intervals. Kanban cards directing production of the particular parts are distributed across the work shift according to the desired heijunka sequence. At the appropriate time, identified by the column header, the cards are withdrawn and the parts they direct be produced are processed within the time interval determined by the next slot with that kanban production instruction.
For example, if Part A is to be produced every hour, B every two hours and C every three hours the box would be made with columns representing one hour intervals and three rows representing the three part numbers. Each slot in Row A would have a card, every other slot in Row B would have a card, and every third slot in Row C would have a card. Every hour at the designated time the cards from the appropriate column would be removed and the kanban instructions followed.
The hijunka box concept can be extended to determine assembly performance to schedule by kitting the parts scheduled to be assembled within identical time intervals. If, for instance, the parts expected to be installed in two hours are collected into a kit that kit would be expected to be empty (and returned for refilling) after two hours. If it is not, the work is known to be behind schedule in enough time to catch back up.