aggregation of a key figure date field in the BEX query

we had a problem of aggregation of a key figure date field in the BEX query ,problem is it not aggregating correctly and sometimes it is displaying "x" ,where those key figures are date fields converted from the normal date format to decimal format in the key figure info object type/unit .

And in the aggregation tab we have standard aggregation as minimum and exception aggregation as "No aggregation(x if more than one record occurs).

I changed this exception aggregation : to "Last value" and tried executing the query now I am able to overcome with problem of "x"'s but still it is not aggregating correctly the key figure values.And the ref. characteristics is 0CALDAY

But I am not sure of what does the "last value" mean for a date key figure like - baseline date .Please let me know what can be done.

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sasi M