Operator Balance Chart (OBC).

A visual tool used to create continuous flow in a process consisting of several steps and staffed by different operators. In an OBC, the operator's work is divided into work elements and plotted against branch time. Also called an operator loading diagram or a yamazumi board . 

In an OBC, the vertical columns are used to represent how much work each operator has to do in total relative to the Takt time. The vertical column for each operator is constructed by stacking together small columns representing individual elements of work. 

The height of each element depends on the amount of time required for it. An Operator Balance Chart can aid in the redistribution of work elements among operators. This is essential if one wants to reduce the number of operators needed by reducing the amount of work for each operator almost