As you’d expect, it relies on a 32.768 kHz crystal to provide a stable clock. Fed into a 4060 binary ripple counter, that clock is divided down 14 times to deliver a 2Hz square wave. This then ...

It’s not the finest of frequency counters, depending as it does on the ATtiny’s clock rather than a calibrated crystal reference, but it does the job. The results are shown in the video below ...