The placement of reference electrodes in solid galvanic cells is discussed. The common flat arrangement with a reference electrode side by side on an extension of the solid electrolyte (SE) is experimentally convenient but poses difficulties in the evaluation of the results. Common interpretation of the measurement introduce an error into the impedances determined. The error may be significant. A calibration method is presented that allows to relate the true impedance to measured signals. It is also shown that in the special case where the extension in the SE can be made thinner than the SE, the placement of the reference electrode side by side introduces only a negligible error. In the case when the current carrying electrodes can be made of equal size, only misaligned, the error can be corrected, to first order, by the use of two reference electrodes and an averaging procedure. (c) 2008 Elsevier B.V. All rights reserved.