Watch Accuracy Deviation Calculator

Work out watch accuracy deviation instantly with clear inputs, formula shown and shareable results.

About Watch Accuracy Deviation Calculator

Daily rate is the total deviation divided by the days observed, then scaled to a month and a year for comparison against manufacturer specifications. COSC chronometer certification allows minus four to plus six seconds a day, so a watch gaining two seconds daily is performing better than most.

Formula

Daily rate

seconds per day = total deviation / days observed

Worked example

With the default values below, Watch Accuracy Deviation Calculator returns Deviation per day of 1.600. Change any input above and every figure here is recalculated in your browser.

Inputs used

Total deviation observedaccepts -600–600 s: 8 s
Days observedminimum 0.1: 5

Results

Deviation per day: 1.600 s
Deviation per month: 48.00 s
Deviation per year: 584.0 s
Accuracy assessment: Chronometer grade

Step by step

1Values used
2Daily rate
3Deviation per day= 1.600 s
4Deviation per month= 48.00 s
5Deviation per year= 584.0 s
6Accuracy assessment= Chronometer grade

Assumptions and limits

The result is derived only from the 2 inputs listed above. Anything not among them is not part of the calculation.
In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
Figures are rounded for display to 3 decimal places, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Watch Accuracy Deviation figure worked out?

seconds per day = total deviation / days observed. Daily rate is the total deviation divided by the days observed, then scaled to a month and a year for comparison against manufacturer specifications.

Why does this matter?

COSC chronometer certification allows minus four to plus six seconds a day, so a watch gaining two seconds daily is performing better than most.

What do I need to enter?

Enter total deviation observed, days observed. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.