Previous Month Money Rate Calculation

Hi,

Can you help me about calculating the previous month and previous year same current month money rate?

I have need three month's USD Money Month Rate :

1) Current Month Money Rate  (I have calculated it by using UserResponse function)

2) Previous Month Money Rate (I am trying to calculate it)

3) Previous Year Same Current Month Money Rate (I am trying to calculate it)

1)

v_CurrentMonth       =UserResponse("[Fiscal Year/Period]")

v_CurrentMonthRate=[Month Rate] Where ([Fiscal Year/Period] = [v_CurrentMonth])

2)

v_Previous Month =v_Previous Month =If(Left([v_CurrentMonth];3)="JAN") Then ("DEC "+[v_Min Year]) ElseIf(Left([v_CurrentMonth];3)="FEB") Then ("JAN "+[v_Max Year]) ElseIf(Left([v_CurrentMonth];3)="MAR") Then ("FEB "+[v_Max Year])  ElseIf(Left([v_CurrentMonth];3)="APR") Then ("MAR "+[v_Max Year])  ElseIf(Left([v_CurrentMonth];3)="MAY") Then ("APR "+[v_Max Year])  ElseIf(Left([v_CurrentMonth];3)="JUN") Then ("MAY "+[v_Max Year])  ElseIf(Left([v_CurrentMonth];3)="JUL") Then ("JUN "+[v_Max Year])  ElseIf(Left([v_CurrentMonth];3)="AUG") Then ("JUL "+[v_Max Year])  ElseIf(Left([v_CurrentMonth];3)="SEP") Then ("AUG "+[v_Max Year])  ElseIf(Left([v_CurrentMonth];3)="OCT") Then ("SEP "+[v_Max Year])  ElseIf(Left([v_CurrentMonth];3)="KSM") Then ("OCT "+[v_Max Year]) ElseIf(Left([v_CurrentMonth];3)="DEC") Then ("NOV "+[v_Max Year]

v_PreviousMonthMoneyRate=[Month Rate] Where (Max([ZSD_MB1_Q001 ].[Fiscal Year/Period])=[v_PreviousMonth])

There are three years = 2015 ,  2014 , 2013.

You can see the Money Rates according to the Fiscal Year/Period as first two columns at the below table.

I am trying to find USD Money Rate for upper 3 months.

Best Regards,