This paper was read at the Conference on Experimental Design held at the Mathematics Research Center, U. S. Army, University of Wisconsin in January 1961, and later appeared inPhysics Today, September 1961. The paper is clearly addressed to both physicistsand statisticiansand for this reason now appears inTechnometricsthrough the kind permission of Robert R. Davis, editor ofPhysics Today. The paper discusses the use of various experimental designs to increase the precision of measurement of physical constants through the detection of systematic errors.