Steren CAL-150 Instructivo De Uso página 215

As you can see, the trace and zoom functions can be used
to locate a specifi c point, press the button in
order to produce a value for the x and y coordinates.
In order to return to the original graph size, press the
button.
Note:
The coordinate values are approximate.
The trace function can only be used immediately after the
graph has been displayed on the LCD screen. This function
can not be used in other calculation modes, except:
The trace function cannot be saved within a program.
Plot Function
This function allows you to plot a point on the screen while
a graph is being displayed. The point can be moves up,