Abstract: The invention relates to a method and apparatus for marking entrance and exit opening sites in opposite surfaces of a wall member of a perforation to extend therethrough and is provided, at one surface at a site corresponding to one of the entrance and exit openings with a wave signal transmitter and, at the other surface with a wave signal receiver responding to transmitted signals by rendering an indication of a maximum strength wave signal as a function of the location of the other of the entrance and exit opening. In a preferred embodiment, the receiver is mounted on a drill or the like at a predetermined distance from the axis thereof and the transmitter is provided with a cantilever provided with a marker spaced from the transmitter at a distance corresponding to the predetermined distance.

Abstract: The invention relates to a depth gauge for use in angling or sports fishery. The depth of a body of water may be measured therewith from its surface to its bottom, and/or the depth and the size of strata of water of different temperatures for the purpose of offering bait to different species of fish in their preferred environments, for instance at the bottom of a water or at a thermocline stratum. In accordance with the invention, a water-proof housing a temperature sensor, a pressure sensor, a digital evaluation circuit, a display and a program switch are provided within a water-proof housing and electrically interconnected in such a manner, that the measurement value about the depth of the water to its bottom and/or water strata marked by temperature differences of more than 3.degree. Kelvin are processed and stored by the digital evaluation circuit. By means of the program switch, the stored measurement data may be called up and rendered visible in the display.