A method for investigating a formation, in particular a pile borehole, comprising: suspending a caliper into a formation such that an axis of the caliper is substantially parallel with the longitudinal axis of the formation, transmitting a transmitted pulse signal from a transmitter on the caliper, wherein the transmitter comprises a sonar head; detecting a reflected pulse signal with a detector on the caliper, wherein the reflected pulse signal is the transmitted pulse signal reflected from a target location on a surface of the formation onto which the transmitted pulse signal is incident; determining the time interval between the transmission of the transmitted pulse signal and the detection of the reflected pulse signal, wherein the distance from the transmitter to the target location on the surface of the formation and back to the detector is the time interval between the transmission of the transmitted pulse signal and the detection of the reflected pulse signal times the speed of the first pulse signal; rotating the transmitter and the detector with respect to the axis of the caliper, wherein rotation of the transmitter and the detector causes the target location on the surface of the formation onto which the transmitted pulse signal is incident to rotate with respect to the axis of the caliper; raising and lowering the caliper in the formation, wherein raising and lowering the caliper in the formation causes the target location on the surface of the formation to raise and lower, respectively; guiding the caliper on one or more guide cables as the caliper is raised and/or lowered in the formation, wherein the one or more guide cables allow the position of the caliper to be controlled as the caliper is raised and/or lowered in the formation; characterized in that any one of: - raising and/or lowering the caliper up and down the at least one of the one or more guide cables by gripping on the at least one guide cable; or - the caliper is fixably attached to at least one of the one or more guide cables and travels with respect to one or more further guide cables to which the caliper is not fixably attached, wherein raising and lowering the caliper comprises raising and lowering the at least one guide cable fixedly attached to the caliper such that raising and lowering the at least one guide cable fixedly attached to the caliper raises and lowers the caliper; or - raising and lowering the caliper comprises raising and lowering the caliper via a cable attached to the caliper. suspending a caliper into a formation such that an axis of the caliper is substantially parallel with the longitudinal axis of the formation, transmitting a transmitted pulse signal from a transmitter on the caliper, wherein the transmitter comprises a sonar head; detecting a reflected pulse signal with a detector on the caliper, wherein the reflected pulse signal is the transmitted pulse signal reflected from a target location on a surface of the formation onto which the transmitted pulse signal is incident; determining the time interval between the transmission of the transmitted pulse signal and the detection of the reflected pulse signal, wherein the distance from the transmitter to the target location on the surface of the formation and back to the detector is the time interval between the transmission of the transmitted pulse signal and the detection of the reflected pulse signal times the speed of the first pulse signal; rotating the transmitter and the detector with respect to the axis of the caliper, wherein rotation of the transmitter and the detector causes the target location on the surface of the formation onto which the transmitted pulse signal is incident to rotate with respect to the axis of the caliper; raising and lowering the caliper in the formation, wherein raising and lowering the caliper in the formation causes the target location on the surface of the formation to raise and lower, respectively; guiding the caliper on one or more guide cables as the caliper is raised and/or lowered in the formation, wherein the one or more guide cables allow the position of the caliper to be controlled as the caliper is raised and/or lowered in the formation; - raising and/or lowering the caliper up and down the at least one of the one or more guide cables by gripping on the at least one guide cable; or - the caliper is fixably attached to at least one of the one or more guide cables and travels with respect to one or more further guide cables to which the caliper is not fixably attached, wherein raising and lowering the caliper comprises raising and lowering the at least one guide cable fixedly attached to the caliper such that raising and lowering the at least one guide cable fixedly attached to the caliper raises and lowers the caliper; or - raising and lowering the caliper comprises raising and lowering the caliper via a cable attached to the caliper.