Creo Simulate > Reference Links > Log Scale
  
Log Scale
Use the Log Scale check box on the X Axis and Y Axis tabs of the Graph Window Options dialog box to change the values on the graph's X or Y axis to a logarithmic scale.
After you select Log Scale for an axis, Creo Simulate converts the values on the appropriate axis to log base 10. If you then deselect the check box, the values return to a linear scale.
Following are the limitations of these commands:
You cannot convert an axis to a log scale if the axis contains any non-positive values.
You cannot change the scale of a graph that is tied to another graph.
You cannot tie two graphs that are not using the same scale on both axes.
For example, if graph 1 uses log scale on the x axis and linear scale on the y axis, and graph 2 uses linear scale on both axes, you cannot tie them in any way. If you change the x axis on graph 2 to log scale, you can then tie the graphs.