math7 timePRECISE TIME

A precise reference for your clocks

Set every clock
to the right second.

This page measures how far your device clock is from accurate time and shows the corrected time, ready to copy into a microcontroller, an RTC chip, or any clock you need to set.

UTC

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Measuring your clock…

01 / Synchronization

How accurate is your device?

The page exchanges several timestamps with the server and keeps the fastest round trip, the same idea NTP uses.

Your device clock

Offset
—
Round trip
—
Accuracy
—
Samples
—

A positive offset means your device is ahead. The accuracy is about half of the fastest round trip, because network delay may not be equal in both directions.

Server time source

NTP status
—
Stratum
—
Server offset
—
Estimated error
—

The server keeps its clock in step with public NTP servers using chrony.

02 / RTC formats

Values ready for your RTC.

Every value below uses the corrected time and updates each second. Copy the one your firmware or chip expects.

BCD registers follow the common DS1307, DS3231, and PCF8563 order: seconds, minutes, hours (24-hour), day of week, date, month, and year. Day of week uses 1 for Monday through 7 for Sunday; check your chip's datasheet for its convention.

03 / Exact second

Hit the second exactly.

The marker flashes at the start of every corrected second. Prepare the time on your device, then press set when the marker flashes.

Next second in — ms

Next minute starts at —

The sound plays through your device, so add the audio delay of your speakers or headphones if you need better than a few milliseconds.

04 / Drift

How far does your RTC drift?

Set your RTC, note the corrected time, and compare again after a day or more. The longer you wait, the more precise the result.

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05 / API

Use the time API.

Both endpoints return JSON and are never cached. Measure the round trip on your side and add half of it to the server time.

curl https://time.math7.com/api/time
{"serverTimeMs":1790777095258}

curl https://time.math7.com/api/ntp
{"synchronized":true,"stratum":3,"systemOffsetMs":0.08,...}