Abstract
A circuit whereby two entirely independent wave forms may be observed simultaneously on the screen of the cathode‐ray oscillograph is described. The two curves to be observed are fed through separate transformers to suppressor‐modulate two 57 vacuum tubes. By a special combination of a thyratron and an ordinary neon diode, a square wave is obtained which is applied to the control grids of the 57's, biasing first one, then the other to cut‐off. Data are given for grid extinction of the thyratron. The uses are discussed and illustrated.

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