Hi Rupert,
Here's an alternate method.
Ian's suggestionis the only one I know using a scatter chart, but Numbers also offers a '2-axis' Category chart. It's the last one on the menu in the Charts button, requires two series of Y values, and defauts to a line chart for the first series and a column chart (vertical bar chart) for the second Y series.
The two (Y) axes may have different scales, and may be formatted separately. Here's an example. Instructions below.
The data columns are column B (X values) and column D (Y values).
Because this is a Category chart, the X values must be listed in a header row, where they will be recognized as 'category labels' . As 'categories', they will be evenly spaced along the x axis, and wil be ordered left to right in the order they appear (top to bottom) in column A of the table.
2-Axis charts require a table with two columns of Y data. To provide the second 'data' set, I've added column C, and filled it with zeroes.
To create the chart, select columns C and D, then click the Charts button and select the Two-Axis chart.
With ther chart selected, open the Chart Inspector.
Choose Axis.
Uncheck "Show Values" using the pop-up menu for Value Axis (Y1)
Check "Show Axis" using the pop-up menu for Value Axis (Y2)
Set min and max values and steps to values that will give you integer labels for the Y value grid lines.
Choose Series.
Click on the colour block (on the table) for the dummy series (Y1).
Set Data Symbol to 'none'. Use the Line thickness control in the format bar to set the line thickness to 0.25 pt and the colour to black.
Click on the colour block for the 'real' series. Set the data symbol and size, and the line thickness as desired.
Regards,
Barry
