The volume of letters sent by households or household originated mail can be obtained from Table 1 by adding the volumes of HH-to-HH and HH-to-NHH mail.
The table simplifies calculation of volume. 
mnli hypothesis: The table simplifies calculation of volume.  premise: The volume of letters sent by households or household originated mail can be obtained from Table 1 by adding the volumes of HH-to-HH and HH-to-NHH mail.