The second (s) is the base unit of time in the International System of Units, defined by the vibration frequency of cesium-133 atoms. It serves as the foundation for all time measurements, from clocks and watches to GPS satellites and atomic physics. One second equals exactly 1,000 milliseconds and is divided into 60 seconds per minute.

The hour (h) is a time unit equal to 60 minutes or 3,600 seconds, the standard measure for work shifts, travel times, and business hours worldwide. Payroll calculations, flight durations, and daily schedules are all structured around hours. One hour equals exactly 3,600 seconds, and 24 hours make up one day.