Machined surface of hard steel parts like gears, bearings, camshafts etc. is full of local imperfections which are commonly described in terms of surface integrity. This surface integrity is usually quantified with the level of residual stresses or amplitude of Barkhausen noise signal for instance. The contribution introduces parameter called Sum of Effective Residual Stresses (SERS) to describe the level of surface damage after grinding. Experimental data obtained by X-Ray Diffraction (XRD) and Barkhausen Noise Analysis (BNA) methods of ground gears are shown. The way to use SERS approach for experimental determination of penetration depth of Barkhausen signal in steels is proposed, too.