[otrs] Graph stats

Hi list, I'm new to OTRS but I succeed in having a working server connected to multiple LDAP for multiple customers. I've played a bit with tickets : create, answer, close or wait for escalation. Unfortunaly, I'm trying to get some graph stats and all I can get is a desperately flat graph. I'd like to create a stat report with : - the last (week or month) on the X axis - the average first response time on the Y axis - a selection of queues as input data. I tried multiple combination but never succeeded. I'm using OTRS 3.0b5 with a mysql DB. Thanks for your help, Ionel