Previous Month Expression

[#1]

Hi,

Please can someone help me with calculating the previous month expression.  I have a straight table with number of licenses calculated by:

sum([Total Licenses])

Against this I want to show the same value for the previous month, so I written the below expression:

=sum({$<[Month Key]={$(=[PM Key])}>} [Total Licenses])

[Month Key] is held on every record to show the month e.g. 3_2012. 

[PM Key] is also held on every record to show the previous month e.g. 2_2012.

but not working :-<

Grateful for any assitance with this.

Mike.

[#2]

Have already tried that - Above only works when the month stay in the correct sort order, and it also goes wrong when the user makes a select that excludes previous month.

[#3]

The sort order thing is true - are you having problems with that? There are ways around sort problems. However, I have a previous month expression in my code and it continues to function even when the month is restricted. What code are you using?

[#4]

I am displaying my table horizontally so don't think the Above() function will work for me.

[#5]

In that case Before() will serve a similar purpose.

[#6]

Sorry, I am acutally using a pivot table rather than a straight table so Above() or Below() will not work.