I have a single X axis and two stacked Y axes. Is there a way to create grid lines parallel to both of the Y axes?
First, create the grid lines for the X axis as normal and specify that the grid lines are to be parallel to the first Y axis. Then, select the X axis and choose Graph | Add to Graph | Duplicate Axis. Place a check mark in the boxes to disable the tick marks and labels. After the axis is created, double click on it and click on the Grid Lines button. Make the grid lines parallel to the second Y axis and click OK. Then, on the Line Properties tab, change the Line Style to Invisible.