Marker 1 Location Use this field to specify the physical location of the first marker in each pair. To Specify the Marker 1 Location Variable: Specify the Input SAS Data Set. All of the variables in the specified input data set are displayed in the Available Variables field. Examine the list of available variables. Highlight the variable listing the location of the first marker in each marker pair. Click to add the highlighted variable to the Marker 1 Location field, as shown below: