1. If the length of "one foot" is 8 cm and the length of the desk is 7 feet, then the length of the desk is 56 cm.

2. Height is also a ruler. If the height is 150 cm, hold a big tree and put your hands together. The length of this tree is about 150 cm.

3. If you want to measure the height of the tree, shadows are also helpful. Just measure the length of the shadow of the tree and your own shadow.

If you want to know how far the mountain ahead is from you, you can ask the sound to help you measure it. Sound can travel 33 1 meter per second, so you can hear the echo by shouting at the mountain and watching it for a few seconds. Multiply the time to hear the echo by 33 1 and divide it by 2.

5. "Astronomical recorder" Coral scientists found that corals record time on themselves: they "paint" a ring pattern on the body wall every day, and "paint" 365 a year, no more or less.