Figure 3: Usable Documents from the Limited Sample

              19xx   Bly  1950  1960  1970  1980  1990  Totals
Total Docs.     10    10    10    22    66   132    99     349
Usable Docs.     5     7     6    16    36    71    61     202

Named Aud.       0     6     2     9    15    39    21      92
Internal Aud.    5     7     4    14    34    70    61     195