If I am Calculating current month total value for tag as TagTot('Total Smelter AC KWH_TTL',BOM('*'),'*'). how should I show previous month last reading?

Try something like this:

TagTot('Total Smelter AC KWH_TTL',BOM(BOM('*')-1),BOM('*')-1)

BOM('*')-1 is the beginning of the current month minus one second; in other words, the end of the previous month.

thanks avanfosson​