15.8.6  LIMITED 

You  may specify the limits over which the histograms are to be added.  If
you specify the Y or Z limits, then all data that contains  values  inside
these limits will be added.  For example if you
     ADD 1 to 2 LIMITED FROM Y=10 to Y=11
But data set 1 contains the followind data:
1,0;  2,10;  3,0;  4,11;  5,0
Points  2  to  4  inclusive will be added, and only points 1 and 5 will be
omitted.