The result of this first step was thus a set of constraints on the accuracy with which CCD model parameters must be determined. The second step in the measurement selection process determined the accuracy with which various proposed laboratory measurements can constrain CCD response model parameters. This step required analysis and simulation of feasible laboratory measurements. In principle, the product of this step was a suite of laboratory measurements that calibrates ACIS CCDs with accuracy adequate to meet scientific objectives. The parametric CCD response model clearly plays a central role in the selection of calibration measurements.
Practical considerations complicate the selection of calibration measurements.
Specific, readily identifiable scientific measurement requirements do not provide a complete specification of calibration accuracy requirements. For these reasons, it is useful to have a clear, if somewhat arbitrary, set of calibration objectives with which to guide calibration planning. The objectives adopted to plan the CCD subassembly calibration measurements described here are therefore stated, though not justified, as part of each measurement description. The complexities of laboratory measurements and the oversimplifications inherent in feasible simulations of those measurements must also be accounted for in calibration planning. To allow for these uncertainties, this plan called for more measurements than the absolute minimum number that simulations suggest was necessary.