Please try the following formulas for the Actual Position and Forecast Position. They match exactly the same values you posted in this thread. Unfortunately, you can’t use these calculated fields in a line chart because they are visual-level calculations and multiple fields are associated with them.
Example:
Actual Position - ifelse({Actuals Start Balance} <> 0, {Actuals Start Balance} + runningSum(SUM({Actuals Amount}),[TransactionDate ASC],[BankAccount]), 0)
Forecast Position - ifelse({Forecast start balance} <> 0, {Forecast start balance} + runningSum(SUM({Forecast Amount}),[TransactionDate ASC],[BankAccount]), 0)
