Sentence:  The transient visualizer used in the past were mostly of types in which the voltage for the time <WSD>sweepage</WSD> is generated by a relaxation oscillation circuit made up of a hot-cathode discharge tube, say, a thyratron, and a condenser, and the control voltage for the generation of the transient to be observed is also generated by the same circuit. 
Meaning of the word marked with <WSD> tags:  The circuit of an oscilloscope used to track the time dimension.