er time.
   As a consequence, the relationship between SCLK and ET or UTC is not
   accurately described by a linear function; usually, a piecewise linear
   function is used to model this relationship.
<P>
 
   The mapping that models the relationship between SCLK and other time
   systems is updated as a mission progresses. While the change in the
   relationship between SCLK and other systems will usually be small, you
   should be aware that it exists; it may be a cause of discrepancies
   between resul