Schedule rotaing with text and numbers
 

I am putting together a schedule where each worker rotates weekly on a shift
that is designated with numbers and text. Such as: 42 A, 42 B, 42 C, etc.

It will be listed in order in a column beside the corrosponding date such as;
The date will be in Column A, and the schedule will be in column B

12/02/2005 42 A
14/02/2005
15/02/2005
16/02/2005
17/02/2005
18/02/2005
19/02/2005
20/02/2005 42 B

This will rotate like this every seven days between A,B,C shifts.

Is there a formula have the A B C calculated atomatically. There are 300
employees and 70 Shifts each with A,B,C and sometimes D shifts.

Thank you in advance
Martin