I want to use super/subscripts in a text. The enhanced postscript terminal can display super / subscript in the labels or axis names. To use this termianl one needs "enhanced" option:
The following is an example to make legends with the superscripts. The functions are y=sin**2(x), y=sin**3(x), and y=sqrt(sin(x)).
When texts in the legend contain super / subscripts, text lines become very close each other. In the example above, the baseline skip was increased to 30% by set key spacing 1.3 . 
I want to use Greek letters in a text. To use Greek letters in a text, you may try using enhanced postscript terminal just like the case of super / subscripts.
The Greek letters can be displayed by {/Symbol a}. This gives "alpha" which corresponds to "a". The relation of the Symbol and alphabet is as follows.
You can also specify various postscript characters by octal codes, for example, {/243} is a pound (L) mark, {/247} is a section mark. See ps_guide.ps which comes with gnuplot source in detail. The next example is to draw the linear function y=Alpha x+ Gamma and two Greek letters with those values in the figure.

How do I adjust an interval between X,Y axes and their labels ? The interval can be controlled by the ofset options of set {xy}label command.
This moves the Xaxis label one letter upward. When you give a positive Y ofset, the X label gets into the graph. While the ofset is negative, distance between the X label and the graph becomes larger. Gnuplot tries to draw a graph as large as possible, so the graph hight becomes larger when the Xaxis label moves upward. On the contrary the graph becomes small when the Xaxis goes downward.
To adjust the Yaxis label, use set ylabel "YAXIS" +n,+m where "+n" and "+m" are the Yaxis ofset options. The following examples are to set the X ofset "+5" and "5". This affects the width of the graph.
