labeled ALT COMP. This switch is used to connect the altitude compensator to the system. The bottom portion of the control box contains four knobs. The two on the left side are labeled BANDPASS. These knobs select the high and low frequencies. The knob labeled REC ZERO is a dual-purpose knob. Turning this knob controls the pen deflection on the recorder. Depressing the knob inhibits system output. The bottom right knob is labeled gFS, and is used to select one of nine sensitivity ranges (from 0.1g to 40g full scale) or self-test. In the TST position, the self-test function will be initiated. AN/ASA-64 SAD Group The SAD group consists of only one unit-the ID-1559 magnetic variation indicator (MAG VAR indicator). This indicator receives the MAD signals from the ECA, along with roll attitude signals. These signals are processed and a SAD mark is generated, which is correlated with the roll input. In cases of excessive aircraft roll rate, the indicator will generate a SAD inhibit signal. This signal illuminates the SAD INHIBIT lights on the selector control panel and the pilot and copilot’s navigation advisory panel, letting the operators know the SAD mark is unreliable. AN/ASA-65 Magnetic Compensator Group The magnetic compensator group consists of the AM-6459 electronic control amplifier (compensator ECA), C-8935 control-indicator, DT-355 mag- netometer assembly, three compensating coils, CP-1390 magnetic field computer, and ID-2254 magnetic field indicator. AM-6459 ELECTRONIC CONTROL AMPLIFIER.— The electronic control amplifier (ECA) processes standard magnetic anomaly detector signals from the MAD subsystems, operator compensation adjustments, and maneuver signals from the magnetometer. The ECA provides compensation currents, which are sent to the MAD boom compensation coils. C-8935 COMPENSATOR CONTROL- INDICATOR.— This control-indicator (fig. 4-28) contains potentiometers for adjustment of the maneuver and correlated signals into compensating terms. The potentiometer outputs are routed back to the ECA to be amplified. From there they are sent to the compensator coil as compensation signals. On the face of the control-indicator there are nine index counters. The top three provide the adjustment index for the potentiometers in the transverse, longitudinal, and vertical magnetometer circuits. They are labeled T (transverse), L (longitudinal), and V (vertical). The other six (labeled 1 to 6) provide compensation adjustment for the T, L, and V magnetometer circuits. The MAG TERM knob selects the magnetic term to be compensated. This knob must be in the OFF position unless compensation is required. The RATE knob selects the speed of the servomotor with 1 being the slowest and 4 the fastest. Across the bottom of the faceplate there are four toggle switches. The POWER-OFF switch provides power to the unit. The SERVO-OFF switch provides both ac and dc power to the servomotor system. This switch must be in the OFF position unless recompensation is required. The UP-DOWN switch provides voltage directly to the servomotor selected. The counter indication will increase or decrease depending on which way this switch is toggled. The +/OFF/– switch provides voltage to the servo system. In the OFF position, the servomotor is operated only by the UP-DOWN switch. DT-355 MAGNETOMETER ASSEMBLY.— The magnetometer assembly contains three coils oriented to sense magnetic strength in each of the basic longitudinal, transverse, and vertical axes. This Figure 4-28.-Compensator control-indicator. 4-22