Calculator

I have four field with a speific value depening on Total,

Total   -  Sum of all

Value 1 - 50% of Total

Value 2 - 40% of Total

Value3 - 10% of Total

Now when we punch the total, all the other field calculate, no dramas.  But I want to be able to also punch an amount in say Value 2 and all other calculate.

I have been racking my brain getting heaps of circular reference's..... anyone got any ideas???

Thanks