Calculator Inputs
Example Data Table
| Case | Reference Elapsed | Local Elapsed | Skew Seconds | Skew PPM | Meaning |
|---|---|---|---|---|---|
| Network sensor | 3600 | 3600.170 | 0.170 | 47.222 | Local clock runs fast. |
| Database node | 7200 | 7199.760 | -0.240 | -33.333 | Local clock runs slow. |
| Lab device | 1800 | 1800.006 | 0.006 | 3.333 | Small drift detected. |
Formula Used
The calculator compares elapsed time from a trusted reference clock with elapsed time from a local clock. The main formulas are:
Reference elapsed = Reference end − Reference start
Local elapsed = Local end − Local start
Clock skew = Local elapsed − Reference elapsed
Skew ppm = Clock skew ÷ Reference elapsed × 1,000,000
Projected drift = Skew ppm ÷ 1,000,000 × Projection window
Optional network offset uses four timestamps:
Offset = ((T2 − T1) + (T3 − T4)) ÷ 2.
Delay uses (T4 − T1) − (T3 − T2).
How to Use This Calculator
- Enter the trusted reference clock start and end readings.
- Enter the local device clock start and end readings.
- Add a tolerance value in parts per million.
- Enter a projection window to estimate future drift.
- Use optional four timestamp fields for network offset checks.
- Press the calculate button to view the result above the form.
- Export the result as a CSV or PDF report.
Clock Skew Analysis Guide
What Clock Skew Means
Clock skew is the difference between two clock rates. One clock may gain time. Another clock may lose time. The error may look small at first. Yet it can grow across hours, days, or months. This matters in logs, payments, distributed systems, analytics, and audit trails.
Why Offset and Skew Are Different
Offset is the current time difference between two clocks. Skew is the rate difference between them. A device may have a small offset but a large skew. That means it looks correct now, but it will drift soon. A clock with stable skew can often be corrected by planned adjustment.
Using PPM for Drift
Parts per million is a common timing measure. It shows how many seconds a clock gains or loses per million seconds. Positive ppm means the local clock runs fast. Negative ppm means it runs slow. This calculator converts elapsed readings into ppm, ppb, hourly drift, and projected drift.
Network Timing Checks
Networked devices may include message delay. Four timestamp analysis helps estimate offset and round trip delay. This is useful when checking device synchronization across servers, sensors, gateways, or monitoring agents. The result should be reviewed with network quality in mind.
Practical Use Cases
Use this tool when comparing server logs, validating sensor timestamps, testing embedded hardware, checking database replicas, or reviewing time correction policies. Enter accurate readings from the same observation period. Longer periods often produce better drift estimates. Short tests can be noisy because small timestamp errors have a larger effect.
Reading the Result
The result shows whether the clock is inside your tolerance. It also shows the projected drift for your chosen window. Use that value to plan synchronization intervals. If the projected drift is too high, shorten the sync interval or inspect the device clock source.
FAQs
What is clock skew?
Clock skew is the rate difference between two clocks. It shows whether a local clock is running faster or slower than a trusted reference clock.
Is clock skew the same as clock offset?
No. Offset is the current time gap. Skew is the drift rate. Offset is a position error. Skew is a speed error.
What does positive ppm mean?
Positive ppm means the local clock is running fast. It gains time compared with the reference clock during the measured interval.
What does negative ppm mean?
Negative ppm means the local clock is running slow. It loses time compared with the reference clock during the measured interval.
Why use a longer measurement period?
A longer period reduces noise from small timestamp errors. It usually gives a more reliable estimate of clock drift and skew rate.
What is projected drift?
Projected drift estimates how much time the local clock may gain or lose over a future window, based on the measured ppm rate.
Can this help with server log checks?
Yes. It can compare server clock behavior, estimate timing mismatch, and support decisions about synchronization intervals or correction needs.
What are the four network timestamps?
They are client send, server receive, server transmit, and client receive times. They help estimate network offset and round trip delay.