Microsecond (µs)
Definition: A microsecond is one millionth of a second.
History/origin: Microseconds became widely used once electrical engineering, audio systems, and computing required more precise timing than milliseconds.
Current use: Microseconds are used in embedded systems, sensors, audio processing, robotics, and data transmission timing.
Year (yr)
Definition: The year is a long calendar unit based on Earth's solar orbit. For unit conversion, it is commonly averaged as 365.25 days.
History/origin: People organized years around seasons, planting cycles, and celestial observations, then refined them through calendars for civic and scientific use.
Current use: Yr is used for ages, anniversaries, mortgages, warranties, leases, climate averages, school grades, investment horizons, history timelines, and long-term records.