Hi Ishana,
Firstly, I'd suggest adding the fiscal period start and end dates to the specification so that you can verify that you are choosing the values you need. The spec code "[10]M" always chooses the 10th month, regardless of the fiscal period chosen from the tool bar. "_[10]M" chooses the period 10 periods ago. Using "[10]M" the figures displayed on the drill down will not change, since you are always choosing the same period.
While you are dealing with the short year, you will need a formula to build the correct code, adding a numeric offset to the fiscal period chosen from the toolbar.
Let me know if you'd like help building the formula.
What you are trying to accomplish is completely doable.
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Andrew Bates