Values (not "labels") are exactly centered on the tick marks with:
goptions reset=ALL
gunit=pct
colors=(black)
ftext=hwcgm001
ftitle=hwcgm009
htext=3
noborder
maxcolors=255
device=CGMOFML
hsize=10 in vsize=8 ;
axis1 value=(a=90 h=3pct) /*order=(0 to 800 by 200)*/ minor=none label=(a=90 color=black "Mean, (ng/mL)") offset=(1);
axis2 /*order=(0 to 80 by 20)*/ minor=none label=(color=black "Time (hr)") offset=(1);
proc gplot data=sashelp.air;
plot air*date / vaxis=axis1 haxis=axis2;
run;
quit;
If you add
format air 8.0;, a shift can be seen. I reckon that may be the reason you see that "buffer": you request a long format, and sas provides it.