Forecast formula in Business Objects

I noticed someone searching for the following : target sales revenue formula

Obviously, it's rather simplistic, but here's a formula to try calculate a future number, when you already have some numbers from the past.

Let's say we had numbers for 4 quarters and 2 years.

2010 Q1 1000
2010 Q2 500
2010 Q3 900
2010 Q4 800

2011 Q1 1250
2011 Q2 800
2011 Q3 800
2011 Q4 700

and we want to figure out, if that trend continues, what the numbers for 2012 will look like. Here's how:

=(sum([Sales] where ([Year]="2010"))  * 0.25) +(sum([Sales] where ([Year]="2011"))  * 0.75)

For Q1 2012, this would give : 250 + 937.5 = 1187.5

Of course, you could add a fraction, based on your own business knowledge, but it's a start.