ADDENDUMAdjustableD.R.R.ForAquaProbe530/540/550SeriesDigitalDepthInstrumentsAs noted on page 9 of the Owner's Handbook supplied with your Aqua Probe Digital Depth Instrument each unit issupplied with an advanced version of Aqua Meter's exclusive D.R.R. (Delayed Receiver Recovery) system. Its purposeis to eliminate random false depth readings due to the presence of "subsurface interference" which consists of numeroussmall particles, air bubbles, and other targets. These subsurface interference causing targets are always present in thearea just below the surface of any body of water and are capable of reflecting ultrasonic sound waves. Generally theechos from sub-surface interference targets are considerably weaker than echos from the true bottom target. Thereforethe DRR circuit causes a reduction of the depth finder's receiver sensitivity to weaker/shallow/targets and allows thesensitivity to recover to normal levels for deeper/stronger bottom targets at a carefully controlled rate.The D.R.R. circuit in your Aqua Probe Digital has been factory calibrated for the optimum level of sensitivity reduction andrecovery rate. As received, the DRR in your unit will eliminate erroneous false readings due to all but the very mostsevere cases of subsurface interference. However, there may be some conditions where field adjustment of the DRRcircuit will be helpful to compensate for abnormal conditions. As an example, if the bottom composition is very muddy andsilty, or if there is heavy growth of marine vegetation (seaweeds) in the area where you do most of your boating, thebottom echo may be very weak. Such a bottom condition will absorb much of the ultrasonic sound waves, thus, requiringadditional receiver sensitivity and a slightly reduced amount of D.R.R. Or as another example, consider navigatingthrough a heavily trafficed channel. In this area, the
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