There is a single command to define the correspondence between the User
Coordinates and the Physical Coordinates.
`LIMITS Xleft Xright Ylow Yup`

by which you specify the User Coordinates values at the left and right ends
of the X-axis and low and up ends of the Y-axis. Note that Xleft may be
greater than Xright. GREG stores all User Coordinates as Real*8 numbers
to allow high precision labelling.

If you have no specific idea about the range of values spanned by your
data, just type `LIMITS`

GREG then automatically computes the extrema of the input data (read by
COLUMN see section 3.2) and adds some reasonable margin to set the limits.
You can mix automatic and fixed limits using the ``wild'' value ```*`''
`LIMITS * Xright * Yup`

will computes automatic limits for the left end of the X axis and low end
of Y axis.

The previous examples set *Linear Conversion* formula between the User
Coordinates and the Physical Coordinates. You can obtain a *Logarithmic
Conversion* formula for the abscissa or the ordinate
using the options `/XLOG` or `/YLOG`
respectively. Note that, contrary to most systems, GREG includes a * true* logarithmic conversion : you do *NOT* have to provide the
logarithm of your data. Also, error bars will be correctly plotted for the
logarithmic conversion : all the necessary computations are done into
GREG .