Filling 2 litre milk cartons

Discuss an 'acceptable' level of variation in a process (due to common causes).

The limits 2000 ml and 2080 ml are pre-specified as acceptable variation in filling the milk containers. Values outside this range are displayed in red — they might indicate special causes.

Drag the slider to see the values appear in order.


How soon would you detect the increasing trend?


The context is a milk bottling plant filling containers with a nominal '2 litres' of milk.

Because of the variability in the filling machine, the actual volume of milk varies and the target is a mean volume of 2040 ml with almost all containers containing between 2000 and 2080ml.

The data are regularly sampled from a shift.