Abstract: A digital oscilloscope automatically selects as the initial instance of a waveform parameter to be measured the instance that is both visible in the displayed trace and closest to the trigger reference point. Such a manner of automatic selection allows a greater amount of panning and zooming while the 'scope is subsequently stopped, without causing a different instance to become the measured instance, and also reduces confusion about continuity of measurement while the display is altered with the 'scope is still running. This automatically selected choice can still be overridden, if desired, by a manual selection. A further refinement is to, once an instance is automatically selected, retain it as the selected instance as long as it remains visible as part of a modified displayed trace, even if it would not otherwise become the selected initial instance if the measurement activity were first initiated with that modified trace.