Science Demands: Effective Area

Undoubted science gains from accurate absolute calibration BUT few objects require absolute flux to better than 10%
- eg hot isolated neutron stars to get Lx, but distance uncertainties dominate
Relative calibration most important; most undesirable are:
- Erroneous gradients, eg for absorption; power-law extrapolation...
- Uncalibrated small scale structure – spurious lines

Undoubted science gains from accurate absolute calibration BUT few objects require absolute flux to better than 10%