Where we use them
A thermometer read −4 °C (degrees Celsius) in the morning. It read 6 °C in the afternoon. How much warmer?
Step 1 of 3
- Morning: −4 °C.
- Afternoon: 6 °C.
- Change = 6 − (−4) = 10.
It was 10 °C warmer. A reading is the number you see at one time.
Rule: change = later reading take away earlier reading.
For the thermometer: 6 − (−4) = 6 + 4 = 10.
A change more than zero means the reading went up. A change less than zero means the reading went down. A change of exactly zero means no change.
| Setting | Earlier | Later | Change | Which way |
|---|---|---|---|---|
| Thermometer | −4 °C | 6 °C | 10 | up |
| Lift | 2 | −3 | −5 | down |
| Quiz score | −3 | 2 | 5 | up |
Why this matters
A change says two things: how big, and which way. A signed number says both.
Slide both readings in the lab. Watch which way it moved.
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