Find main account balance

How can I find main account balance such that start date is the date of the first trans in the account and end date is a certain selected date ? I am trying to use the below code segment , is this right  also,  how can I check if the returned balance  value is correct ?

dimensionAttributeValueCombination= DimensionAttributeValueCombination::find(DimensionAttributeValueCombinationRecID);

mainaccount=MainAccount::find(dimensionAttributeValueCombination.MainAccount);

AccountBalance=mainaccount.getBalance(dateNull(), BalanceAsoffDate,FiscalPeriodType::Operating,OperationsTax::Current);