時間單位

1. second: 1s = 1000ms
2. millisecond: 1ms = 1000us
3. microsecond: 1us = 1000ns
4. nanosecond: 1ns = 1000ps
5. picosecond: 1ps = 1000fs
6. femtosecond: 1fs = 1000as
7. attosecond: 1as = 10^-18 s