S0 MUCH statistical work is performed with approximate data that this writer has long held the opinion that approximate methods also are frequently justified, both for treating the data and for rough checking purposes. Again, where approximate solutions will serve, these may, in many instances, be obtained readily and easily by graphic methods, particularly where the functions considered will plot to straight lines, making interpolation easy.2 Hyperbolic, or reciprocal, grids are a relatively unknown and, for that reason, rarely used type of graph upon which certain functions will plot either as a continuous linear curve or as a broken series of linear curves. For rate studies and for purposes of obtaining weighted arithmetic averages graphically, the hyperbolic grid will frequently render great service. The justification of the present paper is that nearly all standard texts on graphics seem to ignore the hyperbolic grid entirely, or give it inadequate treatment. Perhaps the best generally available explanation of this graph and its usage occurs respectively in the graph paper catalogs of Keuffel & Esser Company, Inc., and of the Codex Book Company, Inc.; and, in the latter, references are made to two articles and to a Codex leaflet which further describe the uses of the hyperbolic grid. To whom should go the credit for having devised this type of graph seems to be unknown, for the present author has nowhere been able to note reference to its originator. Ready-prepared hyperbolic graph papers, conventionally on paper 8X l in size, may be obtained from manufacturers of graph papers, and, on these commercial papers, rulings are sufficiently numerous to provide for reasonably accurate plotting and interpolation. The horizontal axis, or axis of abscissas, is calibrated according to the reciprocals of the numbers printed on this scale. The vertical scale, or axis of ordinates, is customarily graduated arithmetically, and the numerical values given to these graduations may be large or small as desired. The vertical scale is graduated from zero (0) in both positive and negative directions, if desired; the horizontal scale conventionally begins with unity (1) and is calibrated positively to the right to infinity (co).