The number of Zs found by the online filter.
Corrected for sampling fraction and efficiency.
For this special case,
the Oracle Interface Exec actually returns
DAT_B_FOUND * DAT_B_TOTAL / DAT_B_SAMPLED
The data is tagged as invalid if DAT_B_FOUND is -1 or
DAT_B_SAMPLED is zero.
(description supplied by R.Dubois)
The data is read from Oracle SLD_ONLINE.DATLOG.DAT_Z_FOUND
