Exercise 2: sample answer

(a) Record. A dated entry in an account book is a contemporary document, the kind of evidence historians weigh most heavily, although it may only show that a clock was bought, not how it worked.

(b) Legend. Real clocks developed gradually over generations and by many hands, so a story of one man inventing the clock in a single moment is a simplification. Treat "first inventor" claims with suspicion (check any specific claim).

(c) Round number. "The later 14th century" is an honest statement of uncertainty: it points to the period when the surviving evidence appears without pretending to a precise year.