Grapher can create plots with grid lines shared across multiple axes. If you already have your plots created and you just need to turn on the grid lines, simply check Share grid lines on the Line tab of the Property Manager. Otherwise, see the steps below. 

1. Create a plot with multiple axes:
   1. Create a graph of your choice, using the Home | New Graph | <graph type> command. 
   2. Add a second plot to your graph using the Home | Add to Graph | <plot type> command. 
   3. In the Choose Axes dialog, choose to add a new Axis in the X or Y direction as needed and keep the existing axis for the axis you will be sharing the grid lines for. For example, if you'd like to share Y axis grid lines across two X axes, create a new X Axis and do not create a new Y axis. 
   4. Click OK. Your plot should now show a total of 3 axes with grid lines missing on one of the graphs. 
2. Turn on grid line sharing: 
   1. Select the axis you'd like to share the grid lines for (in our example this would be the Y Axis). 
   2. In the Property Manager, click the Line tab. 
   3. Check the box next to Share grid lines. 
      • If you'd like the grid lines to appear over the gap between the axes, check the box next to Lines between axes. 

Method 1: If you don't have many plots, or if your plots are separated by a distance and you don't wish the grid lines to go through the separation, complete the steps below to add grid lines to each Y axis.

1. Click on the X axis to select it.
2. In the Property Manager, click on the Line tab.
3. In the Grid Line Properties section, set the Parallel axis to the first Y axis.
4. Check the box next to Major tick grid line option.
5. Click the Home | Add to Graph | Axis | X Axis command. 
6. In the Position X Axis dialog, toggle At the top of or At the bottom of and select the second Y axis from the list.
7. Check the Disable tick marks and Disable labels boxes to turn off the display of tick marks and labels.
8. Click OK.
9. Click on the new X axis in either the Object Manager or plot window to select it. 
10. In the Property Manager, click the Link Axis tab.
11. Click None in the Link axis field and select the first X Axis.
12. Check the box in the Link axis scale and Link limits fields.
13. Click on the Line tab.
14. In the Grid Line Properties section, change the Parallel axis to the second Y axis.
15. Check the box next to the Major tick grid line option. 
16. In the Axis Line Properties section, expand the Axis line properties and change the line Style to Invisible to turn off the axis line display. Only the grid lines remain.
17. Repeat steps 5-16 for each additional Y axis.

Method 2: If you have many plots, if your plots are right up against one another, or if your plots are separated by a distance and you don't mind the grid lines to go through the separation, follow the steps below.

1. Select the graph or an item within the graph.
2. Click Home | Add to Graph | Axis | Y Axis.
3. In the Position Y Axis dialog, toggle At the left of, and select the X axis from the list.
4. Check the Disable tick marks and Disable labels boxes and click OK.
5. Select the new Y Axis.
6. Click on the Axis tab in the Property Manager.
7. Increase the Length until this new axis is the length of all of the other y axes combined.
8. Click on the Line tab.
9. In the Axis Line Properties section, expand the Axis line properties and change the line Style to Invisible to turn off the axis line display.
10. Select the X Axis.
11. On the Line page in the Property Manager, in the Grid Line Properties section, change the Parallel axis to the new Y axis.
12. Check the box in the Major ticket grid line field, if needed.

Updated March 2020