We have two different Opportunity record types that can be associated to each account. Opportunity record type A has a total amount in it. Opportunity records type B will be entered with smaller amounts. I need to create a field/fields on the account record that inserts the amount of opportunity record type A and then subtracts the amounts of opportunity records type B as they are created.
On Account, create two RSF fields
RecordTypeA_RSF__c = SUM of Opportunities of record type A amount RecordTypeB_RSF__c = SUM of Opportunities of record type B smallerAmount__c
Then create a formula on Account
A_versus_B_Diff__c = RecordTypeA_RSF__c - RecordTypeB_RSF__c
Of course, use better field names than I used to match your domain
You are limited in the number of RSF fields OOB, but you can request more from SFDC Support if you run out