Hey calbears, does the 84 refer to the year you were born? If so, I'm starting to feel old...
As to the UC application, last year both sections had limited room to write, so I divided my info up according to what I wanted to say about different activities. The chronological post secondary history may be more geared to people like me, who were out of school some terms in the middle of undergrad. I used it to put down what I was doing when I was not in school (jobs, or other activities when you aren't in school aren't extracurricular, they're the main event). If I wanted to say more about an activity, specifically the clinically related and community service type things I did, I put them under the "extracurricular, community and activities" where I had more room, and them just mentioned them by name under chronological.
Ex. Activities: Asian Outreach Project. Volunteered for an immunization project targeting vietnamese speaking immigrants. Took health histories, helped families with paperwork, blah blah blah.
Chronological: 1999: Returned to UC Berkeley in January, started at Asian Outreach Project, president of xyz club, blah blah blah.