On-Net Surveillance Systems, Inc.
NetDVMS 6.5f User Manual
Daylight Saving Time
218
Daylight Saving Time
Daylight saving time (DST, also known as summer time) is the practice of advancing clocks in order
for evenings to have more daylight and mornings to have less. Typically, clocks are adjusted forward
one hour sometime during the spring season and adjusted backward sometime during the fall season,
hence the saying spring forward, fall back. Note that use of DST varies between countries/regions.
Clocks are adjusted forward when DST starts
When working with a surveillance system, which is inherently time-sensitive, it is important to know
how the system handles DST.
Spring: Switch from Standard Time to DST
The change from standard time to DST is not much of an issue since you jump one hour forward.
Typically, the clock jumps forward from 02:00 standard time to 03:00 DST, and the day thus has 23
hours. In that case, there is simply no data between 02:00 and 03:00 in the morning since that hour,
for that day, did not exist.
Fall: Switch from DST to Standard Time
When you switch from DST to standard time in the fall, you jump one hour back. Typically, the clock
jumps backward from 02:00 DST to 01:00 standard time, repeating that hour, and the day thus has
25 hours. In that case, you will reach 01:59:59, then immediately revert back to 01:00:00. If the
system did not react, it would essentially re-record that hour, so the first instance of, for example,
01:30 would be overwritten by the second instance of 01:30.
Because of this, NetDVMS will forcefully
archive
the current video in the event that the system time
changes by more than five minutes. The first instance of the 01:00 hour will not be viewable directly
from access clients (NetGuard, NetGuard-EVS and Ocularis Client Lite). However, the data is recorded
and safe, and it can be browsed using the
Viewer
application by opening the archived database
directly.
