When it comes to creating control charts, it's generally good to collect data in subgroups, if possible. But sometimes gathering subgroups of measurements isn't an option. Measurements may be too expensive. Production volume may be too low. Products may have a long cycle time.
In many of those cases, you can use an I-MR chart. Like all control charts, the I-MR chart has three main uses:
- Monitoring the stability of a process.
Even very stable processes have some variation, and when you try to fix minor fluctuations in a process you can actually cause instability. An I-MR chart can alert you to...