Normally, values on a linear or logarithmic scale increase from left to right (or bottom to top). You can change the direction by selecting the Extents/Intervals/Size command on the Options menu and checking the appropriate "Invert" checkbox below "Specify Extents". For example, if your logarithmic scale on the X axis normally extends from 1 on the left to 1000 on the right, check "Invert X" to change the extents to 1000 on the left, 1 on the right.
For 3D data you can achieve similar results by specifying negative scale factors for the appropriate axes with the Contour Options (for surface plots) or Scatter Plot Options (for 3D scatter plots) commands under the Options menu.
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