Examples:

The current data have significant responses to data within 1.5 to 18 keV.

XSPEC> flux          ! Calculate the current model flux over the default range.

XSPEC> flux 6.4 7.0  ! Calculate the current flux over 6.4 to 7 keV.

XSPEC> flux 1 10     ! The flux is calculated from 1.5 keV (the
                       lower limit of the current response's
                       sensitivity) to 10 keV.