A BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view of a breath input unit, of a breath tester incorporating the present invention, with parts brokenaway to show interior parts; FIG. 2 is a block diagram of the inventive system; and FIG. 3 is a detailed diagram, partly in block form and partly in circuit form, of a part of the system of FIGS. 1 and 2.