Using SPC but with variable target/USL
Hi, I am looking for some advice using SPC to monitor Actual Yield vs Planned Yield. Plotting the SPC to measure Actual Yield (%) alone is straightforward, and normally when there's a single fixed value for an USL or a Target, this is also easy to add. However, for each month there's a Planned Yield value and this varies from month to month. The Target or USL seem to require a fixed value - so wh...