You can use the properties of the graph to set the number of major and minor tick marks (X Scale->Range->Minimum, Maximum, Increment, Minor Increment). In older versions of LabVIEW, you may have to do this every time you write new data to the graph. I don't know if this bug has been fixed. Make sure you turn autoscaling on that axis off. If you have more than one X axis, you will need to set Active X Scale before setting the Range values.
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