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In the conventional power tetrode, when operating within the normal range of electrode voltages, changes in plate potential do not appreciably affect the total space current or its division at the grid plane. Furthermore, changes in grid potential, although affecting to a large degree the magnitude of the space current reaching the screen plane, do not alter materially the division of this current between screen and plate. Making use of these facts, and taking into account the effect of initial velocities of emission and contact potential, each electrode current can be expressed in terms of the 3/2 power of an equivalent voltage and an empirical function. These empirical functions can be plotted on a log-log chart in a manner that allows the complete static curve data to be easily determined for any grid, screen, and plate voltage within the normal operating range. Methods of determining experimentally the empirical functions at low power levels are described. A sample log-log chart and an explanation of its use are presented.