Help with rules

Hi,

I am trying to perform calculation as below in a rule,

Expression 1: A.level([loc].top)=B+C

Expression 2: B=A-C

where as A is at week dept chnl intersection and B/C is at week dept intersection. Lets say A has value updated for two channels as 20, 80. B is 100 and C is 0. When create a workbook, load B as 100 and C as 0. A gets values spread as 50, 50. To fix this i want to have base values for A before executing the calc rule. I can add load rule for A but refresh is throwing error. Any idea how to achieve this.