Hi, On a measure, it's possible to choose an average function. But, in my case, this fonction doesn't work. I want to create a custom average by a field. For example: number of employee by month with the following table. Employee number --- Month --- Number SAL0001 2012/12 1 SAL0002 2012/12 1 SAL0003 2012/12 1 SAL0001 2012/11 1 SAL0002 2012/11 1 SAL0001 2012/10 1 Thanks for you help. Max