data a1;
   infile 'U:\.www\datasets512\Ch11ta01.dat';
   input months size stock;
proc print data=a1;
run;

*The c= option specifies color the l= option specifies
  line type.  You do not need to set the color to black
  if you use the goptions colors=(none) command;

symbol1 v=M i=sm70 c=black l=1;
symbol2 v=S i=sm70 c=black l=3;
proc sort data=a1; by stock size;
proc gplot data=a1;
   plot months*size=stock/frame;
run;

Data a1; set a1;
   sizestoc=size*stock;

proc reg data=a1;
   model months=size stock sizestoc;
   test stock, sizestock;
run;

proc reg data=a1;
   model months=size stock;
run;

symbol1 v=M i=rl c=black;
symbol2 v=S i=rl c=black;
proc gplot data=a1;
   plot months*size=stock/frame;
run;