Watch Accuracy Calculator – Seconds Per Day (s/d)
Measure gain or loss against a reference clock, enter the elapsed time, and get a clear seconds-per-day rate with practical context.
How to measure
- Sync your watch to a trusted reference (time signal / accurate phone)
- Wait at least several hours — longer is better (12–24h+)
- Compare again: note seconds fast (+) or slow (−)
- Enter values above → seconds per day
Formula: s/d = (seconds offset ÷ elapsed hours) × 24
One wrist test is not a COSC certificate. Lab rates use multiple positions and controlled conditions.
Context bands (practical)
About −4 to +6 s/dOften discussed in COSC-style mechanical average territory (lab context)
About ±5 to ±15 s/dCommon “solid daily wearer” mechanical range on the wrist
Beyond ±20–30 s/dWorth checking magnetism, regulation, power reserve, or service
QuartzUsually much tighter than mechanical unless battery/circuit issues
Frequently Asked Questions
How to calculate s/d? (offset seconds ÷ hours) × 24.
Good mechanical accuracy? Many wearers are happy near ±5–15 s/d; COSC is a stricter lab standard.
Why does it change? Position, temperature, wind level, magnetism, measurement error.