Autonumber associated with date

Hey guys,
I need your assistance please. if anyone has similiar code and would
like to share please do.

I have table called "tbl ChestLog" has EntryDate field that is set as
date() and another field called "Chest".
EntryDate format is mm/dd/yyyy and Chest is supposed to be a
combination of Julian Date based on the EntryDate and include -001
(autonumber based on date). For example:

EntryDate: 09/20/2010
Chest: 263-001 for first record for that date
Chest: 263-002 for second record for that date
..
..
Chest: 263-010 for last record for that date

EntryDate: 09/21/2010
Chest: 264-001 for first record for that date
Chest: 264-002 for second record for that date
..
..
Chest: 264-010 for last record for that date

I got the code to convert date to Julian date and added "-", but I
need help in autonumbering based on date and start new autonumbering
on the next date and so forth as it is shown above.

Thank you very much

Majic