“Simple Binary Watches with 4 LED(1/5, 2/10, 4/20, 8/40), it mean 5 minute accuracy indicate.
How it’s work?
Every 0.5 sec CPU wake up(cycle iteration time 100 nS) and increase milliseconds value and come sleep mode(3 uA).
If you press button “TIME();” it show hours and minutes(0.5 seconds per value) in binary mode in 4 LEDs.”