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The general points discussed above for the XRT survey are also applicable to the WFC.
The WFC field of view is 
in diameter.
During the survey, the S1 and S2
filters will be used alternately, hence providing two XUV colours
in the waveband from about 60 up to 200 Å (see Table 5.3).
During the survey a source will be scanned for up to
about a minute every 1.5 hours (one satellite orbit), over a interval
of 
days, where 
is the ecliptic latitude
of the source.
The total exposure time at most locations on the sky should thus be
s (after allowing for a loss of about 25 percent due
to high background regions). The available time is divided
approximately equally between the two survey filters, which are
alternated at a frequency of approximately once per day. As the WFC and
XRT are coaligned and are operated for essentially the same time intervals,
the anticipated WFC survey exposure for any point in the sky can be
determined by reference to Figure 6.1 
which shows the XRT
survey exposure. In order to get the WFC survey exposure in either of
the survey filters, the exposures given in Figure 6.1 should
be multiplied by a factor of 3 (because of the larger field of view of the
WFC).
The spatial resolution of the WFC is about 1.4' FWHM
(full width at half maximum) within about
of the optical axis, and for the survey it is about 2.5'
FWHM averaged over the field-of-view.
The location accuracy (error circle 90% confidence radius)
for point sources in the survey varies from 
for the
weakest ones (set by photon counting statistics) to 
for strong
sources (limited by the WFC attitude determination and systematic errors -
some improvement on this may be expected eventually).
