Sharper Image Hadrons SN004 Instructions Manual page 9

Setting the Atomic Time and Date Head H1 or H2
to synchronize. Once it is successful, the clock displays extremely
accurate time and the correct date. A successfully synchronized
clock features a non-blinking antenna icon and a radiating beacon.
The synchronized clock attempts to refresh itself with the radio time
signal at least once a day. If it fails for more than 3 days, the antenna
icon disappears. The clock still functions as a quartz clock until it
can be refreshed again.
The clock is a radio device and, like a mobile phone or the radio,
in certain locations and times of day, it may not pick up a strong
enough signal to synchronize. If the clock fails to synchronize in
the first attempt, it reattempts at the top of every hour until 12:00
a.m. In most cases, the clock synchronizes overnight as the radio
signal is the strongest in the early morning. You can leave the clock
to synchronize at a later time or you can set the clock manually. As
noted below, a manually set clock still attempts to synchronize itself
automatically at the top of every hour.
Note: Regarding forced synchronization and halting of synchroniza-
tion, if you want the clock to attempt synchronization, press and
hold the MODE button. This activates the synchronization process.
If the clock is in synchronization mode, then press and hold MODE
to halt synchronization.