Line of balance

Many projects repeat the same set of activities many times: floors of a tower, houses in a township, kilometres of pipeline or road. Line of balance plans such work by drawing, for each activity, a line showing which unit it has reached at each point in time. The slope of each line is the production rate of that activity.

The aim is to keep the lines parallel, so that each crew can work continuously from unit to unit without catching up with the crew ahead or waiting for it. If a following activity is faster than the one before, its start must be delayed so that it does not run into the earlier crew at the last unit; if it is slower, it can start soon after but the gap grows. A minimum buffer in time or units between successive activities protects against small delays.

Rates are matched by choosing the number of crews. If one crew takes D days per unit, n crews produce about n / D units per day. The required number of crews is the target rate times D, rounded up to a whole crew, which gives an actual rate slightly above target.

Line of balance shows progress more clearly than a bar chart for repetitive work, and it fits lean construction ideas of steady flow. Its limits are that units are rarely truly identical and that it handles non-repetitive activities poorly, so it is often combined with a network schedule.