The By Part graph displays all measurements arranged by part so that you can see the differences between parts. Gage R&R studies usually arrange measurements by part and by operator, but with an expanded gage R&R study, you can graph other factors.
In the graph, dots represent the measurements, and circle-cross symbols represent the means. The connect line connects the average measurements for each factor level.
If there are more than 9 observations per level, Minitab displays a boxplot instead of an individual value plot.
Multiple measurements for each individual part that vary as minimally as possible (the dots for one part are close together) indicate that the measurement system has low variation. Also, the average measurements of the parts should vary enough to show that the parts are different and represent the entire range of the process.