The reader should note carefully that the scale arrangement of Fig. 167 is entirely different from that used in Fig. 166. In Fig. 166, the two zeros fall together as they ordinarily should do in chart work of this sort. In Fig. 167, however, the two scale zeros are not together and the reader is accordingly prevented from interpreting Fig. 167 directly from the location of dots seen in Fig. 166. It would seem as though a better chart could have been made if the isometric chart, instead of being as in Fig. 167, had been arranged with the two zeros together. Such an arrangement would have permitted easier interpretation, for the reader would have secured a more close similarity to Fig. 166. Another possible arrangement which would have been better than that used in Fig. 167 would put the two 100 per cent marks of the scale together, with the zero marks at the diagonally opposite corners. A chart of this nature would show as two mountain peaks, one on each side, with a valley in the center.
Where an actual model is desired more than an illustration, a very convenient, yet cheap, arrangement can be had by stringing beads on separate wires, each mounted in the center of ruled spaces, like those shown in Fig. 166. The number of beads on each wire can represent to scale the data for the particular square at the center of which the bead wire is placed. The heights of the columns of beads on the different wires would then show clearly the facts for any one section of the field in a manner similar to that of Fig. 167. The beads would probably be more generally understood by an untrained person than the isometric drawing of Fig. 167, and it is for this reason that the scheme is mentioned here. The arrangement by columns seen in Fig. 167 is satisfactory for the trained reader, but the separate beads on wires would probably give a less abstract impression, more easily grasped by the average person.
