Download and open the JMP file:
Click on the Saturdays with the Control key down.
This will select all the Saturdays:
Go to the Rows menu, pull to Markers, and select the cross (+) marker:
This will assign the cross (+) marker to all the Saturdays:
Follow the instruction in the Scatterplot tutorial to get the following scatterplot:
Notice that the Saturdays are marked with a "+" symbol.
Compare this scatterplot to that in Figure 2.4, Page 94 of your
textbook.