# Chart2/TrendLines

## Extrapolating of trend lines

• Trend lines should also allow extrapolating. If data ranges from 1 to 5 but that x axes range from -2 to 10, then the trend line should display from -2 to +10.
• In Excel, the setting is called forward forecast and backward forecast.
• covered in http://www.openoffice.org/issues/show_bug.cgi?id=5085

## Trend line equation and coefficients

Before OpenOffice.org 2.4, it is necessary and possible to add the equation manually. The linear regression formula is Y=mX+b, where m=the slope, and b=the intercept. Let's say you're plotting a regression where the X-axis is in A2:A44, and the Y-axis is in B2:B44. Plot your scattergraph and place the regression line as you normally would. Select a cell near the graph, and enter ="Y = " & ROUND(SLOPE(A2:A44;B2:B44);2) & "X + " & ROUND(INTERCEPT(A2:A44;B2:B44);2). That gives you the regression line's equation. In the cell just below the previous formula, enter ="R-square ="&ROUND(INDEX(LINEST(A2:A44;B2:B44;1;1);3;1);2). That will present the r-square value. Select both cells, and choose Edit->Copy.

Now, make sure the Drawing toolbar is visible (View->Toolbars->Drawing). Select the text box, and draw one. Choose Edit->Paste, and clean up the box so that it fits the text. Click outside the text box. Select the text box again, and move it onto the graph area where you want it to be displayed. (I usually put mine under the legend.) You can then dress up the chart, the text box, and the legend for presentation. When you're done editing, and have the box looking nice, then select the text box. Hold down the shift key and select the graph area. Right-click, and choose "Group."

You can now select the chart, and copy and paste it into Writer, Impress, or Draw documents as you wish.