WSPR Beacon - Frequency and Drift Data

I have been running my Propeller WSPR beacon over night and have gathered 42 data reporting points on drift and frequency as reported by WSPR 2.11 over a 7 hour period.  The beacon is transmitting every 10 minutes and idle between times.  The only temperature control is to wrap the device in foam.

The charts below are are showing the frequency reported by WSPR 2.11, which as I understand it will be the first frequency it decodes and the amout of drift from that frequency over the life of the transmission.

 There are a few somewhat wild excursions initially, but then over time the initial frequency appears to drift upwards with each successive 10 minute period as the device cools.

The amount of drift once the transmission begins is in the opposite direction and after some initial jitter assumes asymptotic behavior at a consistent 2 hertz downward drift as the device warms up.

While none of these figures is horrific, good engineering would indicate that for this kind of application, careful attention to thermal stability is important.