The other day I come to know that the field Legacy Move In Date (field EVER-EINZDAT_ALT) on the contract is not just an information only field. It is used in the meter estimation procedure to determine the vacant period.
What is the vacant period? Well, the SAP code is looking at the date when the device was installed and the validity periods of the contracts for that installation. In the case of the migration contract, it is not using the move-in date for that contract but it is using the legacy move-in date for that contract. Then if there is a vacant period which overlaps the base period the system basing the estimate on, the vacant period is subtracted from the whole base period. In other words, SAP considers that in a vacant period the consumption is zero.
So next time you cannot explain the way SAP calculated an meter reading estimate it can be worhwhile to check this side of the estimation equation.
If you are having an interest in SAP IS-U you can check out my sap-isu community at http://www.sap-isu.net .