Multi-Vari Chart:

In quality control, multi-vari charts are a visual way of presenting variability through a series of charts. The content and format of the charts has evolved over time.

As originally conceived, the multi-vari chart resembles a Shewhart individuals control chart with the following differences:
• The quality characteristic of interest is measured at two extremes (around its diameter, along its length, or across its surface) and these measurements are plotted as vertical lines connecting the minimum and maximum values over time.
• The quality characteristic of interest is plotted across three horizontal panels that represent:
• Variability on a single piece
• Piece-to-piece variability
• Time-to-time variability
• The quality characteristic of interest is plotted against upper and lower specifications rather than control limits. The three panels are interpreted as follows:

Panel	Condition	Corrective action
Variability on a single piece	Lengths of the vertical lines (i.e., the range) exceed one-half the specifications (or more)	Repair or realignment of tool
Piece-to-piece variability	Excessive scatter	Examine process inputs for excessive variability—lengths of the vertical lines are estimates of process capability
Time-to-time variability	Appearance of a non-stationary process	Examine process inputs or steps for evidence of shifts or drifts