...and here's the same test with a crystal-clocked Arduino-clone. I used a Freetronics "Eleven" board, which is very similar to the Uno I used in the previous test.
The results are within tolerances quoted for typical crystals. Compared to the resonator-clock:
- the average error is 43ppm, 47x better
- the temperature stability is approximately 0.28ppm/C, 35x better
For context 1 minute per year is about 2ppm.
The average frequency stability over 25 hours was better than the measurement error, which was 0.6ppm. This implies that, unless the temperature is controlled to within about +/-1C, long-term stability is determined by temperature variations.
