Extending Trendlines and Changing Where Y-Axis Crosses

Question

Hi,
I'm trying to create a graph for a class in school. I've created a scatterplot with a linear trendline through my data. Now I would like to extend that trendline to continue past my data points. I know that in Excel you can simply forecast the trendline. Obviously I have Numbers, not Excel, so I was wondering if there was anyway I could do this.
Also, my x-axis includes both positive and negative numbers. However, the Y-axis does not cross the X-axis at 0. Instead the labels for the Y-axis are on the far left of the graph. I'm trying to move the Y-axis so that it crosses through the 0 point of my Y-axis.
Any help would really be appreciated!
Thanks

Answer 1

amondray556 wrote:
I've created a scatterplot with a linear trendline through my data. Now I would like to extend that trendline to continue past my data points.
Also, my x-axis includes both positive and negative numbers. However, the Y-axis does not cross the X-axis at 0. Instead the labels for the Y-axis are on the far left of the graph. I'm trying to move the Y-axis so that it crosses through the 0 point of my Y-axis.
Hi 'ray,
Numbers will not extend a trend line beyond the last data points, so you'll need to calculate these points. Fortunately, FORECAST uses the same calculation as used for a linear trend line.
Add two rows to your table, one above and one below.
In the first, enter the minimum x value to which you want to extend the trend line (in the example, -10 in D4)
In the second, enter the maximum x value to which you want to extend the trend line in the example, 15 in D14).
In the Y data column, enter the formula shown into the new top and bottom cells (changing only the first cell reference to match the row).
In the example, I entered these formulas into the next column, then copied and pasted values into the Y data column.
The two new data points are points that lie on the extension of the trend line, and will not affect that line beyond extending it. They will, unfortunately, generate data point symbols at each end of the line.
I've also used the Chart Inspector to set the maximum and minimums for each axis to accomodate the data, and the number of steps to ensure whole number indices, including zeroes, on each axis.
Numbers places the "axes" and lables at the bottom and left of the chart, and without detaching the chart from the document, they aren't moveable.
The (red) x and y axes on the example are lines inserted using the Shapes button, then placed on the grid lines from the two zero values. The grid lines can be removed after placing the lines. After placing the lines, I selected lines and chart and did Arrange > Group to allow moving the chart as a unit. I also found that allowed me to resize the chart without losing the alignment of the new axes.
Regards,
Barry