How is it demonstrated to everyone? Not everyone has two standards.
Best I can think of is logic buffer a 10MHz crystal to drive the pic chip running DT timer,
run a 1Hz flashing LED with the timer,
and also fan out the 10MHz clock signal to a cascaded bunch of frequency dividers to achieve
an independent hardware pulse per second derived from the very same crystal.
Then accuracy of the crystal is then a non-issue, and the two LEDs stray away from each other relatively quickly,
when the constant value is incremented by one, they will remain as synchronised as they were in the first place.
It really doesn’t take long, but is there an easier way?