The change in slope of a bore, conduit or pipeline is determined by supporting a pair of pivotally interconnected rigid components in the bore with the ends of the components and the pivotal interconnection therebetween located on the centerline of the bore. The change in slope between the components at the pivotal interconnection therebetween is detected, and this change in slope, because of the manner in which the rigid components are connected, is the same as the change in slope of the bore or pipeline in which the rigid components are placed and is in proportion to the strain in the surrounding pipeline. Apparatus is provided for determining the change of slope in a bore, in this manner, and is particularly adapted for use in pipelines being laid or retrieved.