Conventional sampling techniques yieldminimum risetime in the oscillography of repetitive electrical waveforms. However, system timing uncertainties introduce drift and jitter errors, which are typically comparable in magnitude to thecathode-ray-oscilloscope risetime. By using two sampling oscilloscopes in cascade it is possible to reduce the drift by a factor of 10–3, down to a level of 10-14seconds (during an averaging and recording time interval of 2 minutes). Successive sampling also allows accurate jitter filtering. With the aid of a tunnel-diode step generator the total system has a 10–90 percent risetime of 25 X 10–12 second, a step response that is closely integral Gaussian, a time-measurement uncertainty of about 10-13second, and amplitude accuracy of 0.2 percent. Absolute time calibration is possible with a 3 X 10-14-second resetting capability. Applications include the measurement of the impulse-response functions of coaxial two-port networks in the 10-11-second range. Finally, it is shown that amplitude averaging of a sampled waveform with time jitter causes convolution error and loss of resolution. Copyright © 1970 by The Institute of Electrical and Electronics Engineers, Inc.