Very often we would benefit from some visual method of alerting us to the fact that some process is becoming critical and needs our attention. One such visual aid is a “fever chart”.
Fever charts can be used for any situation where we want to keep track of a process to ensure it is running within acceptable bounds.
- Buffer stocks in front of a production station.
- Steps in a project.
- Stages in a production cycle.
- Project buffers for Critical Chain Project Management technique.
Critical Chain Project Management (CCPM) Buffer Consumption
CCPM (see CCPM article) is a replacement for the well-known Critical Path Method that attempts to schedule the events in a project to complete as rapidly as possible.
CCPM has the added advantage that it takes into account the resources involved as they can often be the constraint that delays a project.
Central to CCPM is a project buffer where ‘spare’ time for the various resources is warehoused.
As that project buffer is consumed, a fever chart in the style below provides a visual warning of impending problems.
As long as we stay out of the “red” zone, the project will finish on time. If we are in the red too long, remedial action might be required.
A chart like this is easily understood by all staff.
A group of several such fever charts – one per project – can be a visual dashboard displayed in public places so that all can continually monitor the well being of the company’s projects at any time.
Buffer and Stock Control
A fever chart can be used to measure the availability of a particular resource such as the buffer in front of a constraint (see Drum, Buffer, Rope article) or inventory stock on hand..
In the chart below, we start in the green (safe) zone and begin consuming the stock on hand.
This moves us to the warning (red) zone and ultimately into the danger (black) zone.
The entry into the black zone is a visual warning to replenish the stock on hand. This brings us back to the red and almost to the green zone.
The advantage of this chart is that it is easily understood by everybody and the action can be made very clear. “If we get into the black, produce 10 items of Part A unit and we get into the top of the red or the bottom of the green zone”.
This type of flag/signal is useful in Kanban scheduling systems (see Kanban article).