A chart that displays the variance within units, between units, between samples and between lots. It is useful in detecting variation sources within a process.
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. Multi-vari charts were first described by Leonard Seder in 1950, though they were developed independently by multiple sources. They were inspired by the stock market candlestick charts or open-high-low-close charts.
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.