Where these numbers turn up
A lift panel shows B2, B1, G, 1, 2, 3. B means basement, a floor under the ground. G is the ground floor. It is the zero of the building.
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Step 1 of 4
- Six lift buttons.
- Floors 1, 2, 3 are above ground.
- G is the chosen zero.
- B1 and B2 are −1 and −2.
The rule
Every number line needs a zero. We choose where it is. In a building, zero is the ground floor. Floors above are 1, 2, 3. Floors below are −1, −2.
On a thermometer, zero is where water freezes. A cold morning can be below it. A reading of −3°C is 3 degrees below zero.
Example
A game team has 3 points. The team loses 5 points. Walk 5 steps left from 3: 2, 1, 0, −1, −2. The score is now −2.