Zone Weights.

—To determine the proper zone weights the influence curve is plotted as in [figure] on page 319. The base line, AB, is divided into as many parts as it is desired to have zones; from the mid-point of each part a perpendicular to the base line is erected to meet the curve, shown in the table, as mid-ordinates. These are each multiplied by 100 and divided by the longest, in the case of five zones, 94.85, to get them into percentages of the whole. These are now adjusted to near numbers for easy multiplication. For example, to multiply by 33¹⁄₃ add two ciphers and divide by 3; to multiply by 25 add two ciphers and divide by 4; and so on.

Five-zone Table

Zone	Mid- ordinate	Per- centage	Weight	Adjusted Weight		Sum
1	31.62	33.3	33.3	33	¹⁄₃	33	¹⁄₃
2	54.77	57.7	24.4	25		58	¹⁄₃
3	70.71	74.6	18.9	16	²⁄₃	75
4	83.67	88.5	13.9	15		90
5	94.87	100.0	11.5	10		100

To get weights for six zones take the mid-ordinates at 8¹⁄₃, 25, 41²⁄₃, 58¹⁄₃, 75, and 91²⁄₃, as follows:

Zone	Mid- ordinate	Per- centage	Weight	Adjusted Weight		Sum		Another Adjusted Weight		Sum
1	28.86	31	31	30		30		33	¹⁄₃	33	¹⁄₂
2	50.00	52	21	20		50		20		53	¹⁄₃
3	64.45	67	15	15		65		16	²⁄₃	70
4	76.70	80	13	12	¹⁄₂	77	¹⁄₂	10		80
5	87.02	91	11	12	¹⁄₂	90		10		90
6	95.73	100	9	10		100		10		100