For my report I would like to have crystal pull up the previous months sales data.  So for example if this month is October 2009, then I would want September 2009 sales.

But I've come across a problem that I need help with, let's say that the current month is January 2010, then I would want Sales data for December of 2009.  I don’t know of a formula since I would be pulling data from the previous year.

So if here is my basic formula that I have.  (I need help with the first line).

If Month (CurrentDate)=1 then (Need help here);

If Month (CurrentDate)=2 then {IM9_ItemSalesDetailWhse.QtySoldPeriod1};

If Month (CurrentDate)=3 then {IM9_ItemSalesDetailWhse.QtySoldPeriod2};

If Month (CurrentDate)=4 then {IM9_ItemSalesDetailWhse.QtySoldPeriod3};

If Month (CurrentDate)=5 then {IM9_ItemSalesDetailWhse.QtySoldPeriod4};

If Month (CurrentDate)=6 then {IM9_ItemSalesDetailWhse.QtySoldPeriod5};

If Month (CurrentDate)=7 then {IM9_ItemSalesDetailWhse.QtySoldPeriod6};

If Month (CurrentDate)=8 then {IM9_ItemSalesDetailWhse.QtySoldPeriod7};

If Month (CurrentDate)=9 then {IM9_ItemSalesDetailWhse.QtySoldPeriod8};

If Month (CurrentDate)=10 then {IM9_ItemSalesDetailWhse.QtySoldPeriod9};

If Month (CurrentDate)=11 then {IM9_ItemSalesDetailWhse.QtySoldPeriod10};

If Month (CurrentDate)=12 then {IM9_ItemSalesDetailWhse.QtySoldPeriod11}

else 0