A measurement device was developed that evaluates and displays the bending deformation of a crane with long horizontal extension used for construction work in a railway tunnel. The purpose is to adjust the crane rail vertically so that the trolley can move on a straight and smooth path. An array of inclinometer sensors measures the tilt angles along the machine. Piecewise interpolation with polynomials of third and second order is used to reconstruct the bending curve of the crane rail. The computer language Python with its library packages provides a good platform for the implementation of the algorithms, the user interface and the communication task. Evaluation is not done with the machine control hardware, but with a separate, rugged Rasperry Pi running under Linux operating system. With the optical display of the interpolated curve on a touch screen the operator is able to adjust the crane for the construction work.