In version 10, it is possible to set a "visual" target on a dashboard component. So, if you are displaying the number of calls made, you can set a "target" for that dashboard component. This target is stored in the dashboard component configuration, so it shows up by displaying a line on the dashboard.
You can fast forward to section 57/77 for the target setting if you don't want to wathc the entire 10 minutes. Note, while the Tour mentions that this is a useful feature for opportunities dashboard components, it actually works for activities as well (calls etc)