Bandwidth, sample rate, and memory depth are the most common specifications engineers evaluate when they select a digitizing oscilloscope. However, waveform update rate is another important factor to consider. The rate at which an oscilloscope acquires waveforms and updates the display determines the probability of capturing random and infrequent events such as glitches. This application note uses a debugging application—an attempt to capture a random and infrequently occurring metastable state—to illustrate the importance of waveform update rates. Using various acquisition modes, we also compare the waveform update rates of four competitively priced portable oscilloscopes with bandwidth up to 500 MHz from three different vendors.