Related Clues:
- Eventful timeline divisions
- Significant timespans
- Significant spans
- Statistical concerns for pitchers
- Historical study
- They're sometimes named after presidents
- Serbians have no ISBN this time or the last
- Historic blocks of time
- Stats that are better when they're low
- Meaningful stretches
- Sections of a natural history museum, maybe
- History book sections, say
- Geologists' periods
- Paleozoic and Edwardian, e.g
- Long periods of history