I work 6 hrs/day and get one 10-minute break. The law says I should get a break for every 4 hours worked, or for each major fraction thereof. What exactly constitutes "a major fraction?" Does 1/2 of the 4 hours qualify?

The DLSE has interpreted "major fraction" to mean anything MORE than 2 hours. Thus, if you work exactly 6 hours, you would be entitled to only ten minutes of break. If you work anything more than 6 hours, you would be entitled to 20 minutes of break.

You can read the opinion letter here: http://www.dir.ca.gov/dlse/opinions/1999-02-16.pdf