Drawing an average line on a line chart

[CognosInMaine]

Have a line chart with two values being drawn on it. I want to draw two more lines that are an average of these two values. So far every attempt I've tried has failed. When I'm expecting an average value of around 600 I'll get an average line showing a value of something like .7.

How would I do something like this? I've tried various calculations on the desired data items with no luck.

Thanks

[leahmarie]

If none of that is working, there are markers that you can use and it will automatically calculate a mean.  I don't know if that will help you or not.  But if you select the chart in the properties pane underneath chart annotations and select markers there are options you can choose and you can make your own calculation there as well. Worth a shot. I used it once to do a minimum and it worked fine.