What Is NTP? How Internet Time Synchronization Works
Learn how NTP (Network Time Protocol) keeps clocks synchronized across the internet, why accurate time matters, and how Clockzilla uses NTP for precision.
Why Accurate Time Matters on the Internet
Accurate time synchronization is critical for nearly everything on the internet. Financial trading systems require microsecond precision — a trade timestamped incorrectly could be worth millions. SSL/TLS certificates rely on accurate time to validate security. Distributed databases like Google Spanner use synchronized clocks to maintain consistency across data centers worldwide. Even everyday activities like two-factor authentication codes depend on your device's clock being within 30 seconds of the server.
What Is NTP (Network Time Protocol)?
The Network Time Protocol (NTP) is one of the oldest internet protocols still in active use, designed in 1985 by David L. Mills at the University of Delaware. NTP synchronizes computer clocks over a network by exchanging timestamps with time servers. It can achieve accuracy within a few milliseconds on local networks and within tens of milliseconds over the public internet. NTP uses a hierarchical system of "strata" — Stratum 0 devices are atomic clocks or GPS receivers, Stratum 1 servers connect directly to those, and so on.
How NTP Calculates Time Offset
NTP works by exchanging four timestamps between your computer and a time server. Your computer records when it sends a request (t1) and when it receives the response (t4). The server records when it received the request (t2) and when it sent the response (t3). Using these four timestamps, NTP calculates both the clock offset (how far off your clock is) and the network round-trip delay. The formula accounts for the fact that network travel time in each direction may not be equal.
The Stratum System
NTP organizes time sources in a hierarchy called strata. Stratum 0 consists of high-precision timekeeping devices like atomic clocks, GPS receivers, and radio clocks. Stratum 1 servers are directly connected to Stratum 0 devices — these are the primary time servers on the internet. Stratum 2 servers synchronize from Stratum 1 servers, and so on up to Stratum 15. Each level adds a small amount of potential error, but even Stratum 3 servers are typically accurate to within a few milliseconds.
How Clockzilla Uses NTP Principles
Clockzilla implements a simplified NTP-style synchronization engine directly in your browser. It sends requests to multiple time sources (TimeAPI.io and Cloudflare) through a backend proxy, measures the round-trip time for each request, and calculates your local clock's offset from true UTC time. To improve accuracy, Clockzilla takes multiple samples across several rounds, removes statistical outliers using Median Absolute Deviation (MAD), and computes a weighted average that favors the lowest-latency measurements.
Why Your Computer Clock Drifts
Your computer's clock is driven by a quartz crystal oscillator that vibrates at a specific frequency. However, temperature changes, voltage fluctuations, and manufacturing imperfections cause this frequency to drift over time. A typical computer clock drifts by 0.5 to 2 seconds per day. Your operating system periodically syncs with NTP servers (usually once a day on Windows, or continuously on modern macOS and Linux), but between syncs, your clock gradually becomes less accurate. Clockzilla measures this exact drift and shows you how far off your computer clock is at any moment.
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