A digital clock showing seconds is not necessarily accurate. It may have been set incorrectly, lost network synchronization, or drifted because its oscillator runs slightly fast or slow. You can test a phone, computer, wall clock, camera, or audio recorder with a simple comparison.
Choose a Live Reference
Open an independent source that shows the exact time now. Keep the reference and the device visible together. If you are testing a computer, use a second device for the reference so browser rendering and the system clock are not coming from the same source.
Compare at a Clear Boundary
Watch for the reference clock to roll over to the next minute. Note when the device under test reaches that same boundary. A difference under a second may be display or network latency. A consistent difference of several seconds means the clock is offset; a difference that grows over time indicates drift.
Measure Drift, Not Just Offset
- Record the initial difference in seconds.
- Leave the device running normally for 24 hours.
- Compare it again using the same reference.
- Subtract the original offset from the new offset.
If a wall clock was two seconds fast yesterday and seven seconds fast today, it gained about five seconds in 24 hours. Resetting it hides the symptom but does not change that rate. A battery replacement may help a quartz clock; phones and computers usually need automatic network time enabled.
Special Case: Recording Equipment
Cameras and recorders can have correct-looking clocks but still differ from one another. Before a multi-camera shoot, film the same reference clock on every camera. The visible timestamp gives an alignment point and exposes devices that are set to the wrong time zone.
Repeat the check after changing batteries, travelling, or installing an operating-system update. Accuracy is a measured relationship to a reference, not the number of digits on the display.