As recently stated on hackaday:
“A timepiece is rather a rite of passage in the world of hardware hacking”Presenting: A personal time base.
Depending on current location, elevation, and velocity we all experience very real time dilation effects. Time does not pass at the same rate for everyone. The “Project GREAT” experiment in 2005 measured a 20 to 30 ns shift during a weekend family trip to Mt Rainier.
The idea is to continuously monitor and record cumulative time deviation.
This project uses a Rubidium atomic frequency standard to continuously track local time dilation effects relative to:
Electrical Frequency Controlled (EFC) Ovenized Crystal Oscillator (OCXO)
GPS with battery backup for internal RTC
WWVB US atomic clock radio frequency signal
(3) x Temperature Compensated RTC modules with independent battery backup
Thanks to comments from Doc Pedersen and nsayer, I ordered an Electrical Frequency Controlled (EFC) Ovenized Crystal Oscillator (OCXO) with TTL output to improve the short term stability.
It is a muRata OC2545-DT 10.00 MHz OCXO Crystal Oscillator.
Thanks to the commenters I now have some new parts on hand:
muRata OC2545-DT 10.00 MHz OCXO Crystal Oscillator
12 bit i2c DAC board (To generate the control voltage – Delta Sigma w/Filter)
Adafruit Si5351 Clock Generator Breakout (To generate microcontroller clock)
RS232 to TTL converter board
For more detail: Rubidium Disciplined Atomic Clock