### The User Coordinates

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 .