capacitors are supplied, an 8 mfd and a 10 mfd. When the instrumentis shipped, the 10-mfd capacitor is connected in thecircuit in anticipation that this value of capacitance will place PC within range. If PC is not within range, it can be brought in range by changing values of capacitance. Increasing the capacitance will increase the sensitivity and conversely. Several values of capacitance can be obtained by using the capacitors singly or together: used singly, 10 mfd and 8 mfd are available; series connection of the capacitors yields 4.4 mfd, and parallel connection yields 18 mfd. Third, the sensitivity may also be adjusted by changing the zero setting of the Sensitrol relay. This method should be used only as a last resort. As previously stated, both the PT and PC circuits energize PTR. The sequence of oper- ation from that point follows: PTR picks up and energizes RR. RR picks up and energizes LR, which in turn (1) deenergizes PTR, (2) starts the electric motor, (3) starts the electric clock, and (4) energizes a solenoid to operate other instruments that may be used. PTR then drops WMUAIOLAL MAOBMI Us LUG CACCUUILG LARBEL LUCCUANLS IN, out and deenergizes RR and LR. The ETM may be removed from the DFOC by unplugging the two Cinch Jones plugs and removing four screws from the backplate. When this is done, the motor and clock maystill be operated by throwing the “Auto-Man” switch on the motor mount assembly to the green position. C.3 GENERAL COMMENTS The ease or difficulty of sensitivity settings depends to a large extent upon the expected increase in light intensity above the ambient intensity at the particular position in question. If the expected increase is very large, then the sensitivity of both circuits can be set low, eliminating possible premature triggering by shadows or reflections. However, if the anticipated increase in intensity is to be only slightly above the ambientintensity, the settings become critical. If the operation is to occur at dawn or dusk or any time other than a period of maximum ambient light intensity (i.e., high noon), the PC circuit sensitivity can be set quite low and still be triggered by a faint flash of light. If the flash of light occurs at any time other than a period of maximum ambientlight intensity, then the actual light-level differential will be greater The lower the ambient intensity, the greater the differential becomes and the less sensitive the PC circuit needs to be. Thus the PC circuit could be set up to operate on a light-intensity change of less than 1 sun and yet would not be operated by the noonday sun. The foregoing is not true of the PT circuit. It must be desensitized to a point where the brightest anticipated sun will not operate it. Thus it appears that the PT circuit can be utilized best at positions relatively close to the source; the PC circuit can, under the conditions outlined above, be effectively utilized at much greater distances.