Abstract: The invention concerns apparatus for measuring the inclination or gradient of a plane or line. The objective of the invention is apparatus for measuring the inclination or gradient of a plane or line with respect to a predetermined reference plane, comprising a generally rectangular or trapezoidal frame equipped with three outer bearing surfaces disposed at right angles one to another along three of the sides of said frame, a device integral with said frame, sensitive to variations in position in space of said apparatus and which can output a signal proportional to the angular deviation between one of said bearing surfaces and said reference plane, and means of displaying the value of the measurement taken by said sensitive device.