Crystal Reports - Sales journal cross tab report by product code and accounting period

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I'm fairly new to Crystal but have created a Crystal Cross Tab Report to show sales by product code using Receivable.Invoice_date as a parameter and using group options in the cross tab expert to shows sales by calendar month in each column.

However because my company's monthly accounting periods are based on a 4,4,5 week calendar the sales values are not shown in line with the accounting period.

I have tried to link the Financial_Period and Account_Period tables so that I can use Year and Period to group sales by column. What appears to happen is all the sales for the dates specified keep repeating in every accounting period/year.

Does anybody know if / how I can link the accounting year and period to Receivable table so that a cross tab report can be generated by accounting period?