A visual tool that displays the workload of operators in a production process in relation to the takt time. The OBC shows at a glance whether the work is evenly distributed among operators, where there is excess or insufficient capacity, and where there is room for redistribution or improvement. Also known as an operator loading diagram or Yamazumi board. Yamazumi is Japanese for “stacking,” a reference to the diagram’s stacked column structure.

Structure In an OBC, each vertical column represents a single operator. The column is constructed by stacking small blocks on top of one another, with each block representing an individual work element. The height of each block corresponds to the time that element takes. The total column height indicates how much work the operator in question performs in total. A horizontal line at the level of the cycle time immediately shows which operators are working below, at, or above the cycle time.

Application The OBC is a tool for redistributing work elements among operators, for example, when the number of operators required needs to be reduced, or when a process is redesigned following a change in the cycle time. By shifting work elements from one column to another, it is possible to calculate how the work can be distributed most efficiently, with each operator’s workload as close as possible to the takt time. This also serves as a starting point for kaizen: elements that take an excessive amount of time or do not fit well into the flow become immediately visible in the OBC.

For a more detailed process analysis that also takes cycle times and machine operations into account, the OBC is often supplemented with the Standardized Work Combination Table.

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