Exact Time

How is it measured?

When the page opens, it asks AlarmTimer's server (on Cloudflare's worldwide network) for the current time seven times. It also measures each request's round-trip time and assumes the server read its clock halfway through that trip, then compares the result with your device clock. The fastest of the seven round trips is used, because a shorter trip means a tighter estimate. NTP, the standard internet time protocol, works on the same principle.

That's why the result always comes with a measurement error (±). A 40 ms round trip means the true offset lies within 20 ms either side of the value shown. On shaky Wi-Fi the error grows — press Measure again if a value looks odd.

Why are device clocks wrong?

Computers and phones keep time with a small quartz crystal, which can drift a few seconds a day with temperature and manufacturing differences. Devices correct this by syncing with internet time servers. Phones are usually accurate thanks to the mobile network, but Windows by default syncs only about once a week, so a PC can drift several seconds — and much more if syncing is off or the motherboard battery is weak.

• Windows: Settings → Time & language → Date & time → Sync now, and turn on Set time automatically.
• macOS: System Settings → General → Date & Time → turn on Set time and date automatically.
• Phones: turn on automatic date and time.

Exact time vs. "server time"

The big clock is your device time corrected against an internet time server, so it is very close to official time within the error shown. Ticket sales, course registration and flash sales, however, open by that website's own server clock, which may differ from official time by a few hundred milliseconds. Correcting your own clock first at least prevents losing out because your computer was 30 seconds behind.

FAQ