COSC Chronometer Mean Daily Rate
Official ISO 3159 / COSC chronometer certification criterion: the arithmetic average daily rate across 5 positions over the initial 10 days of testing at 23°C must stay between -4.0 and +6.0 s/d.
\[ \bar{R} = \frac{1}{10} \sum_{i=1}^{10} R_i \quad \text{where } -4.0 \le \bar{R} \le +6.0 \text{ s/day} \]
Plain Text Formula:
Mean_Rate = (Sum of Rates over first 10 days) / 10
📐 Variable Definitions & Parameters
| Symbol | Variable Name | Standard Unit | Physical Definition |
|---|---|---|---|
| \[ \bar{R} \] | Mean Daily Rate | s/day | Average daily timing error across first 10 days |
| \[ R_i \] | Daily Rate on Day i | s/day | Measured rate against atomic reference standard clock |
💡 Worked Engineering Example
Problem Statement:
A movement scores daily rates summing to +22.0 seconds over 10 test days. Verify if it meets COSC mean daily rate.
Step-by-Step Solution:
- Compute mean: +22.0 / 10 = +2.20 s/day
- Check bounds: -4.0 <= +2.20 <= +6.0 s/day
🎯 Result: The movement passes the COSC mean daily rate specification with flying colors (+2.2 s/day).