For a given set of epoch time inputs, the Earth Orientation (EO) 
Matrix Calculator will generate a corresponding set of direction 
cosine matrices (or quaternions) which relate vectors whose 
components are written in the terrestrial frame to the celestial frame.

Suppose one has a vector in space,  r_itrf, whose components are written 
in the ITRF (International Terrestrial Reference Frame).  That same vector
in space can have components written in the ICRF (Internation Celestial 
Reference Frame), r_icrf.  The equation relating r_itrf to r_icrf 
is as follows:

   r_icrf =  [C_itrf2icrf] * r_itrf

The quantity C_itrf2icrf is the direction cosine matrix which transforms
the components of r_itrf to r_icrf.  So, the Earth Orientation Matrix
Calculator will generate the C_itrf2icrf at each requested epoch time.