The probe inclinometer is deceptively easy to use. Its use has become increasingly commonplace, but what influences accuracy is less known. This paper describes the charactristics of four systematic errors that can occur and provides some guidance for recognizing and correcting the errors. The strongest asset of the traversing probe inclinometer is its ability to detect a "spike" in the data correspnding to shear displacement in the ground. Overall tilting or distributed displacement of the inclinometer casing is more difficult to evaluate because of the higher potential for systematic errors dominating the results. Reading errors and occasional mistakes also produce apparent displacements. Threfore the data analyst must evaluate the error potential and creen the results for errors.