I was made aware of one inaccuracy in my comment and I cannot edit any more so here goes: The research was on the variations of "quasar radio intensity", not p

I was made aware of one inaccuracy in my comment and I cannot edit any more so here goes: The research was on the variations of "quasar radio intensity", not pulsar frequency. The scientists formulated a model to statistically predict intensity variation and used those projections as their "clock".