You can do this with Set Analysis, but I would suggest trying simpler (and better) ways first. If you load all your data, and in addition a Master Calendar, you could define a relative month in this calendar: 0 for this month, -1 for last month, etc. All you then need to do is to select month -18 to -1.
You can do this with Set Analysis, but I would suggest trying simpler (and better) ways first. If you load all your data, and in addition a Master Calendar, you could define a relative month in this calendar: 0 for this month, -1 for last month, etc. All you then need to do is to select month -18 to -1.
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