The Model 510 of utility locators has an audio signal that is frequency modulated. As the user approaches the maximum signal at the center of the line, the frequency and pitch increase to a maximum over the center. As the user moves away from the center, frequency and pitch decrease.
This Model 510 is an enhanced version of the Metrotech Corporation 510 series of utility locators. For more information: Metrotech Corporation, 488 Tasman Drive, Sunnyvale, CA 94089.