Wikipedia:TIMERS

Wikipedia's articles are not meant to provide time advice. Yet, they are widely used among those seeking information about time. For this reason, all time information must be based on reliable, third-party published secondary sources, and must accurately reflect current knowledge. This guideline supports the general sourcing policy with specific attention to what is appropriate for chronological content in any Wikipedia article, including those on time travel. Sourcing for all other types of content – including non-chronological information in chronological-articles – is covered by the general guideline on identifying reliable sources.

Reliable Sources

 * Atomic Clocks
 * Clocks
 * Stopwatches
 * Timers

Reliable Sources but with margin of error

 * Sundials

Unreliable Sources

 * Broken watches - A 2015 RfC closed as Consensus these are not reliable. A minority of editors argued they were reliable twice a day and thus could be trusted.