Show Trendline (Parameter "show_trend")

Also have a look at rest of parameters...

Chart Parameter: {flashchart title="Revenue 2000 to 2009" width="80%" height="350" type="line"
show_trend="1" show_regression_formula="1"
data="file" file="data/linedata.txt" x_legend="Year 200x" y_legend="Revenue in 1000€" legend_fontsize="11" line_animation="0" tooltip="in 200#x_label#: #val#"}sample0015{/flashchart}

{flashchart title="Revenue 2000 to 2009" width="80%" height="350" type="line" show_trend="1" show_regression_formula="1" data="file" x_legend="Year 200x" y_legend="Revenue in 1000€" file="data/linedata.txt" line_animation="0" tooltip="in 200#x_label#: #val#" legend_fontsize="11"}sample0015{/flashchart}

Notes:
The displayed trendline has been calculated by flashChart's builtin regression feature. The legend (key) "Trend" has click-attribute "toggle-visibility" asigned - if you click it, the trendline will be hidden or displayed.

Important:
If you want to test this sample via copy/paste, ensure that you paste with option "paste as plain text" otherwise imbedded html-codes may invalidate your input.