On-chip variation (OCV)
Beginner
Tiny manufacturing differences that make identical parts on the same chip run at slightly different speeds.
Novice
Small manufacturing differences that make identical cells on one chip run at slightly different speeds. Timing tools allow for it by assuming one path runs a few percent slow while the path it is compared with runs a few percent fast (for example, late delays ×1.05 and early delays ×0.95).
Expert
A flat derate applies one factor everywhere; AOCV scales the factor by path depth and distance; POCV gives each cell its own delay sigma, stored in the library as LVF. Clock paths are derated too, which is why a long unshared clock path costs slack.