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Each event detected with the HRI is time tagged with a precision
of 61 
sec relative to the ROSAT spacecraft clock.
The processing time for determining the position of an event
is dependent upon the event location between the readout taps in
the crossed grid charge detector and varies from 0.36 to 1.35 msec.
For an event rate of 100 counts s 
, the dead time losses
will vary from 4 to 15 percent.
The standard dead time correction formula can be used:
where 
is the true rate,
n is the observed rate, and 
is the dead time per event.
The dead time varies linearly with position, but since source photons
will be recorded over a distribution of fine positions due to
spacecraft motion and the point spread function of the telescope,
there is no single value of dead time for a particular source
observation.
As a first approximation, it is possible to use a typical value
of 
msec.
A separate scalar on the HRI counts preprocessed events
with a dead time of only 30 
sec.
The contents of this scalar are entered into the telemetry
once each second as secondary science.
Thus if the HRI is observing a bright source, the intensity
as derived from the processed events in the image can be
corrected for the dead time using the data
rates determined from the secondary science scalar.