The paper presents the results of an on-going research regarding the optical scanners with rotating, plane or polygonal mirror, used in the on-line, dimensional industrial measurements. Altough this particular area of applications is considered, the results that have been obtained are also valid for others, different kinds of applications of the laser scanners. The parameters of the two devices considered are deduced, in a comparative look, in a rigouros mathematical approach, different from the one in the state-of-the-art. The sources of errors in the scanning process are analysed, and from this, several new solutions for the reducing or for the compensation of the errors are obtained. The main problem presented is the non-linearity of the functioning characteristic and the possibilities of linearizing it - both for the plane and for the rotating mirror device. From the discussion, a designing calculus of the polygonal scanners results, on different cases, with regard to the requiered value of the duty-cycle. The study is completed, for each scanner, with an experimental part, that verifies the theoretical results.