A Comparison of Self-Setting Clocks

What is the self-setting feature of a clock?

Ideally, it is the ability of a quartz clock 1) to automatically set the time correctly when it is first used, and 2) to keep accurate time over the course of its use. Other practical considerations include time zone, daylight saving time, power outage recovery, and connectivity requirements.

Types of self-setting clocks

Self-setting clocks can be based on different synchronization technologies.

‘Atomic’ clocks (narrowly referring to consumer products called WWVB Radio Controlled Clocks)
GPS clocks
Wi-Fi clocks

atomic clock

gps clock

reason clock

Comparison of self-setting clocks

	Atomic clocks	GPS clocks	Wi-Fi clocks
Source of the correct time	periodic sync signals from NIST radio station	GPS satellite signals (highly accurate time is a ‘by-product’ of GPS)	Requires Wi-Fi connectivity and communication with NTP time servers
Common functionality	Periodically synced with the correct UTC time
Device-dependent functionality	Correct for time zone and daylight saving time; power outage recovery
Coverage area	Most places in North America	Worldwide, wherever GPS covers	Worldwide, wherever there’s access to Wi-Fi and the Internet
Indoor signal strength	Depends on geographical location and which room	Can be greatly affected by which room it is in	Only depends on the Wi-Fi signal strength and Internet connectivity
Speed of sync for the first time	Usually longer than 1 minute and can take up to 5 minutes	Depends on the TTFF of the GPS receiver in the clock. 2 to 4 minutes typical	Very fast. Less than a minute

Nomenclature

NTP - Network Time Protocol
NIST - National Institute of Standards and Technology
UTC - Coordinated Universal Time (that is, the time kept at the Prime Meridian that passes through Greenwich, England.)
TTFF - Time to First Fix
LF - Low Frequency

References

Appendix: LF radio antennae of NIST radio station (photo credit: NIST)