The set ylabel command sets the y-axis label. The position of this label depends on the terminal, and can be one of the following three positions (the position can be adjusted with optional parameters).
1. Horizontal text flushed left at the top left of the plot. Terminals that cannot rotate text will probably use this method.
2. Vertical text centered vertically at the left of the plot. Terminals that can rotate text will probably use this method.
3. Horizontal text centered vertically at the left of the plot.
The EEPIC, LaTeX and TPIC drivers use this method. The user must insert
line breaks using 
to prevent the ylabel from overwriting
the plot. To produce a vertical row of characters, add 
between every printing character (but this is ugly).
Syntax:
set ylabel {"<label>"} {<xoff>}{,<yoff>}
show ylabel
With no parameters, the label is cleared. Specifying constants <xoff> or <yoff> as optional offsets for the label will move the label <xoff> or <yoff> character screen coordinates. For example,
set ylabel -1
will change only the x offset of the ylabel, moving the label roughly one character width left of its default position. This is especially useful with the LaTeX driver.
(The EEPIC, Imagen, LaTeX, and TPIC drivers allow 
in a string to specify
a newline.)