Electrical impedance tomography is a procedure by which one finds the conductivity distribution inside a domain from measurements of voltages and currents at the boundary. This work addresses the issue of stability and resolution limit of such an imaging device. The authors consider the realistic case where only a finite number of measurements are available. An important feature of their approach, which is based on linearization, is that they do not discretize the unknown conductivity distribution. Instead, they define a pseudo-solution based on least-squares. A goal of this investigation is to compare the stability and resolution power of a system that uses dipole sources, with another that uses trigonometric sources. Findings are illustrated in numerical calculations.