/*  Example using uniform random number generator to obtain  */
/*  D values uniformly distributed in 2-cm d classes.    */
Data one;
  input dclass freq;
cards;
6   4
8  12
10 20
12 18
;
data two; set one;
retain seed 555; /* <== initialize seed to any value */
  do i=1 to freq;
    value = dbhclass - 1;
    dbh = round(value + 2*uniform(seed), 0.01);
    output;
  end;

我不知道上面标红的是啥意思？请帮我解答下，谢谢！