Very basic breakdown of 121 domestic rules,

8 hours max, of flight time between rest periods. Min rest of eight hours, may be more depending on flight time.

No more than 30 hours in seven days. 24 hours off every seven days.

100 hours max in any calendar month. 1000 hours in a calendar year.

16 hours max duty. Flight and duty times are seperate.

The flight times listed are scheduled maximums and may be exceeded under certain conditions.

Where I work, UAL, the times are tracked in a computer. The crewdesk often knows I'm going illegal before I do.