Measure Change Across a Longer Timeline

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Learn the skill

Use the year labels, not the number of events between them. Subtract dates for elapsed time. A timeline can show that one event followed another without proving that the first caused the second.

Worked example

An event in 1880 and one in 1905 are 25 years apart. Crossing a century boundary does not change subtraction: 1905 - 1880 = 25.

A dated timeline places a library opening at 1972 and a park opening at 1980, separated by eight equal yearly intervals. — On this evenly spaced example, subtract the earlier year from the later year to find elapsed years.

Millford's Fictional Records

A practice timeline lists four events: a mill opened in 1880, a station opened in 1905, a bridge was replaced in 1920, and a museum opened in 1955. No reasons for these changes are recorded here. Use whole-year differences between the dates.

Question 1 How many years passed from the mill opening to the station opening? Answer

Question 2 How many years passed from the station opening to the bridge replacement? Answer

Question 3 How many years does the entire timeline span, from its first event to its last? Answer

Question 4 Which pair of neighboring events has the longest gap? Mill opening to station opening Station opening to bridge replacement Bridge replacement to museum opening

Question 5 Does the sequence alone prove that opening the station caused the bridge replacement? Yes; any earlier event causes the next one No; order alone does not prove a cause Yes; the gap is less than 100 years