Related Clues:

• Divisions of eons
• Important stretches
• The Eisenhower years and others
• They're historical
• Times long gone?
• Important blocks of time
• Presidential administrations, e.g
• Figs. always expressed to two decimal places
• Geologic slices of time
• Schoolmaster assists only some of these characters in periods
• Parts of history books
• Different rooms in a museum, maybe
• Historical topics
• Royal reigns, e.g
• Periods for historians