"The minerals that make up the rocks and soil here will show a pattern. We'll mark the pattern on this plastic screen." Rick indicated a circle of white plastic, scaled like the face of the oscilloscope. "Then, when we go hunting, we'll be looking for deviations from the pattern. For instance, there probably is no metal in the ground here. We're looking for metal. When we find it, the blip on the scope will stand out very plainly. Got it?"
"Think so. Sounds easy. Let's see it work."
Rick held the tip of the probe at waist level. Tony adjusted the controls until the scope flickered bright green. A vertical line on the face of the scope was a much lighter green, nearly white. Then, as Tony switched the activation circuit, the vertical line formed a pattern that varied in width from top to bottom. Here and there a blip, a clear horizontal line, thrust out both ways from the center.
The present pattern was not unlike that of a stylized Christmas tree, with broad blips representing branches at the base, and increasingly narrower ones representing the branches at the top. Rick quickly sketched the pattern on the plastic circle.
"Now watch," he said, and put his rifle on the ground under the probe.
The Christmas tree pattern developed a new element that ruined the design. It was a strong blip, thrusting out from center, about halfway up the pattern.
"Steel," Rick said. "Other metals with good reflection qualities would show blips slightly higher or lower on the scale."
"Some gadget," Chahda said admiringly. "What else you need know?"
"That's all." Tony was already closing the cover to the control panel. "We're ready to move. Rick, suppose we just set this stuff in the back of the jeep instead of disconnecting it? Chahda could carry the probe."
"Good idea. Then it will be ready for use."