In this paper, experimental results of wind tunnel easurements for conventional, symmetrical airfoil NACA 0012 obtained from the trisonic wind tunnel of Aeronautical Institute VTI Zarkovo, Belgrade are presented. The measurements of lift coefficient and lift-curve slope are presented. The results were obtained from tests and integrations of surface static-pressure data over a model of the NACA 0012 airfoil section. Data for the NACA 0012 airfoil were obtained for a free-stream Mach number range of 0.25−0.8 and a chord Reynolds number range of 2×106 to 25×106. The essential results of these measurements along with the results from other authors are presented and evaluated. The principal factors which influence the accuracy of two-dimensional wind tunnel test results are analyzed. The influences of Reynolds number, Mach number and wall interference with reference to solid and flow blockage (blockage of wake) as well as the influence of side-wall boundary layer control are analyzed. Interesting results brought to light the Reynolds number effects of the test model versus Reynolds number effects of the facility in subsonic and transonic flow as well as the effects of the side-wall boundary layer control and wall interference.