timeadjustment

Time adjustment refers to the process of bringing a clock's displayed time into alignment with a reference standard or desired time. It can be performed manually by a user or automatically by devices and systems that obtain time from external references. The goal is to minimize clock errors in offset (the difference between the device clock and the reference) and drift (the gradual change in offset over time).

Two primary methods are used to apply adjustments. Slewing gradually changes the clock rate to reduce offset without jumping the time, preserving continuity in timekeeping. Stepping applies a large, instantaneous correction to jump the clock to the correct value, which can cause a brief discontinuity but quickly eliminates large errors. Many systems use slewing for small discrepancies and stepping for large ones or when a precise start time is required.

Time references and sources are central to time adjustment. Coordinated Universal Time (UTC) is the standard basis for civil time values, with occasional leap seconds added to stay in sync with Earth’s rotation. Time can be derived from highly stable references such as atomic clocks or global navigation satellite systems (GNSS) like GPS, Galileo, or GLONASS. Local devices may further apply time zone rules and daylight saving adjustments, which themselves modify displayed civil time.

Protocols and technologies support automatic synchronization. Network Time Protocol (NTP) and its more precise variant (PTP, IEEE 1588) are common in networks, while Simple NTP (SNTP) serves simpler needs. In critical environments, hardware time stamping and dedicated time servers improve accuracy and reliability.

Applications range from personal devices and databases to telecommunications and financial trading systems. Challenges include clock drift, network latency, leap seconds, time zone changes, and security considerations in time synchronization.