Don Klipstein wrote:

Cheaper still requires oscillators regulated by component tolerances -
and oscillators tend to have at least two components affecting frequency,
and finest tolerance of ones easily available at premium prices is 1%,
meaning low chance of achieving timing highly reliably better than 2% in
either direction unless either crystal or power line time base is used.

I'd have thought getting the cycle to within 10% would be more than
adequate.

Sylvia.