Good day everyone. I once again need advice on, what is to me a very irritating change request. We have the current scenario: We have a value (let's call it DiffValue) that is calculated using the difference between PlanValue - AllocatedValue. This is done per week. I.e. DiffValue = PlanValue - AllocatedValue. Now the request is to do a calculation (let's call it DiffValue4Weeks) for the total DiffValue of the preceding four weeks. The problem is we have information stored like this: OTBYear (which is self-explanatory, i.e. 2010 for example). OTBWeek (which would be the retail week 18 of the year 2010 for example). Weeks are stored per year in order 1 through 52. For a new year it starts again at 1, etc. The calculation initially seemed simple enough until we realized there could be a problem. What if you are in week 3 of a year? E.g. Year 2010, Week 3. How would you cater for that as the 4 weeks necessary for the calculation would be weeks 1, 2 and 3 of 2010 and then week 52 of 2009. I hope this makes sense.