Measure the repeating interval

Measure the repeating interval — guided practice

Estimate the interval between comparable events and predict another one.

The synthetic dip centers are at days 1, 4, 7. These values come from the lowest sample in each group; limited sampling makes them approximate event centers.

1. 1. Record the center times

   InC 9:C11 write Center 1, Center 2, Center 3. Enter 1, 4, 7 in D9:D11. Enter =D10-D9 in D12 and =D11-D10 in D13, with interval labels in C12:C13.

   You should see: Both measured intervals equal 3 days.

   Comparing successive intervals tests whether the pattern is consistent.

2. 2. Estimate the period

   Enter Estimated period in C14 and =(D11-D9)/2 in D14. Explain that two complete intervals separate the first and third event.

   You should see: The estimate is 3 days.

   Dividing the total span by the number of intervals avoids an off-by-one error.

3. 3. Make a conditional prediction

   Enter Next center in C15 and =D11+D14 in D15. Write: if the pattern continues, the next center is near day 10; the fixture ends at day 8 so this is a prediction.

   You should see: The next predicted center is 10 days.

   A prediction outside the data is not an observed fourth event.

4. 4. Test a changed center

   In a separate note, try centers 1, 4, 7.2. The gaps are 3 and 3.2, and the first-to-third estimate is 3.1. Record that irregularity could reflect measurement uncertainty, a timing change or an incorrect pattern. Keep the original cells unchanged.

   You should see: A small change alters the period estimate and its confidence.

   Checking sensitivity discourages false precision.