The Laboratory for Precise Measurement of Length, which is at the same time the National Laboratory for Length (in text 'Laboratory') takes part in CIPM MRA (Comité International des Poids et Mesures, Mutual Recognition Arrangement) comparisons of length standards, which include line scales as very important standards of length. In order to participate in the CIPM MRA key comparisons, Laboratory initiated technology project TP-02/0120-16 "The device for calibrating measurement scales" in 2003, in which a measurement device was constructed. This measurement device has been used in this research. During 2008, applicant was using this device to research calibration 100 mm measurements scale, participating in the EURAMET Key Comparison, EURAMET.L-K7 ''Calibration of line scales'' (a project shared by the leading calibration institutes in the world). In preparation for comparison measurements as a part of technology project mentioned above, NPL line scale length of 100 mm was purchased and it has been calibrated in PTB (Physikalisch-Technische Bundesanstalt, Germany) by the author of this paper. This line scale was used for studying repeatability and reproducibility of measurement results and for the cognition of evaluation of achievable measurement uncertainty. After completion of the project in which have been achieved results fully compatible with the results of other measurement institutes, each factor of measurement uncertainty was separately analyzed by conducting experimental measurements and simulation studies. As a part of research on the impact of measurement uncertainty the following was investigated: the position of laser light sources and optical components, minimizing Abbe's error, the determination of the middle line of line scales, alignment of line scale and laser beam, straightness movement of table, pitch, roll and yaw angles, environmental conditions affect the laser wavelength and the geometry of device and the impact of losing focus while moving of table. After performed experimental measurements and simulation studies in order to analyze the parameters of uncertainties, the modification of system was performed by applying special sliding supports, and the system is completely thermally isolated. After modification of the system, reevaluation of measurement uncertainty was performed, which has been validated in comparison measurements of line scale length of 300 mm with a prestigious international measurement institute.