Hello Christoph,
This model is expecting one single row per quarter. So you need to aggregate the records beforehand. You need something like this
Quarter,Quantity
2007-Q1, 10
2007-Q2, 12
2007-Q3, 11
2007-Q4, 13
2008-Q1, 12
2008-Q2, 14
2008-Q3, 13
2008-Q4, 15
It is also important that the data is sorted in this order.
Greetings
Andreas
