Hi Arup,
You need to compare the previous value until the previous-12 value and check if all of them are below the threshold to display the measure.
Here is an example where I used a measure named [Value]. I also assumed that my threshold was 500 and I checked the last 5 previous reading.
The formula is: =If (Previous([Value];1) < 500 And Previous([Value];2) < 500 And Previous([Value];3) < 500 And Previous([Value];4) < 500 And Previous([Value];5) < 500) Then [Value]
And my report looks like:
Didier