[en] Horizontal drift chambers of a relatively simple and inexpensive design are described. Four of these, each with an active area of 0.89x0.49 m², constitute the basic detector system for a new focal-plane polarimeter at the medium resolution spectrometer (MRS) at TRIUMF. The inherent left-right ambiguity in the direction of drift was resolved using the ∝15% difference in the signals induced on adjacent (odd or even) cathode wires. With separate charge integration of the pulses, a normalized and corrected odd-even difference is obtained from which the horizontal drift direction is reliably deduced. The odd-even difference is found to depend sensitively on the accuracy with which the anode wire is centered in the unit cell. (orig.)