Since we started adding Leap Seconds in 1972, there have been 26 of them - with the 27th to follow at 11:59:59 p.m. UTC (6:59:59 p.m. ET) on Dec. 31, 2016. The most recent addition occurred on June 30, 2015, which was the first since 2012 and the second since 2008. None were added from 1999-2004, but one was added every year with only five exceptions from 1973-95.
Through the use of a Stratum 1 NTP server, it is possible to produce surveillance videos with timestamps legally-traceable to UTC. This solution is far more cost-effective and accurate than others, and has quickly become the preferred option for video surveillance applications.
A GPS NTP server synchronizes to precise time from GPS satellites and operates securely behind a firewall to synchronize all elements of a system, down to the millisecond. Indeed, such servers typically have a margin of error of just plus or minus two milliseconds, which is more than accurate enough for successfully defending time-stamped evidence in a court of law.
Network Time Protocol (NTP) is an open standard Internet protocol that utilizes standard Ethernet wiring to synchronize computers, clocks, networks and other systems to an NTP reference server. The signal can be transmitted over LAN and WAN wired networks and over various wireless systems.