Scoposcopy: Rigol DS1054Z Power Computation, Measurements, Range
Here’s a demonstration of why you have to be careful interpreting the “measurements” or “numbers in boxes” that are delivered to you by most Digital Oscilloscopes. They generally compute the measurements based on the data that is shown on the screen, not the full data in the memory buffer. This can lead to errors caused by partial waveforms in the display.
The Rigol also has the ability to select a portion of the screen using cursors to make the measurements. So using the cursors to select an exact integer number of periods of the waveform leads to greater accuracy in the measurements.