Inside the CS990XD are two separate detectors operating simultaneously. An inland detector which is factory set to ignore mineralised inland ground & give positive response to all metals & a beachdisc detector operating at the adjustable wet salt sand exclude level which gives a negative response to iron. By using the switches on the front of the 990XD to combine the signals from the above two detectors it is possible for the operator to detect all targets whilst eliminating the effects of the ground while distinguishing between good & reject targets. Detection is indicated by the loudspeaker sounding off located in the rear of the battery compartment & by the needle movement on the front panel.