How do you interpret and apply simultaneous requirements in complex GD&T applications?

Simultaneous requirements (SIM REQT or implied by default in ASME Y14.5-2018) require all features controlled to common datums be verified in a single setup maintaining the same datum reference frame. This ensures worst-case functional relationships between features. Application involves: identifying all features sharing common datum references, designing inspection fixtures/CMM programs to measure all features in single setup, understanding that verification failure requires complete re-measurement, and recognizing when separate requirements (SEP REQT) is more appropriate. SIM REQT is critical for functional assemblies where multiple features must mate simultaneously.