[Illustration: FIG. 3.--READS 19,800 CUBIC FEET.] Figs. 1, 2 and 3 represent different states of the index usually employed on the three, five and ten light meters, the sizes commonly found in our dwellings. The smaller dial, placed centrally above the other, is known as the ‘proving dial,’ and, being used merely for testing purposes, is not considered in reading the gas consumption. Although the index dials vary in nomenclature as well as in number, it is generally safe to consider that if the name is placed _above_ the dial a complete revolution of the pointer is required to register the amount of gas indicated by the name; whereas if the name is placed _below_ the dial each numbered division of the dial represents the amount corresponding to the name. If doubt still exists as to the value of each division of the lowest or right-hand dial, remember that no meter index is designed to read less than one hundred cubic feet for each division of the circle. After one has indexed his own meter for a month or two he is in a position to begin checking the bills presented. The ‘present state of meter’ and the ‘previous state of meter’ are always specified, and the mere subtraction of the former from the latter gives the consumption. This is not invariably the case, however. After a meter has registered its maximum reading--100,000 in the smaller sizes--it passes over the zero point and begins to build up a new record. This happens at intervals as long as the apparatus is kept in service. Before me lies a bill giving the ‘present state’ as 1,700 and the ‘previous state’ as 96,300. Since the meter was continuously employed, it must have registered up to 100,000, so that it registered 3,700 cubic feet on the old score before recording 1,700 cubic feet on the new. Consequently, adding 1,700 to the difference between ‘previous state’ and the highest possible reading gives 5,400 cubic feet--the amount consumed during the month. By reading one’s own meter the detection of any error on the part of the indexer or of the clerical force at the gas office becomes possible. Errors of this nature are of rare occurrence, as those who have adopted this plan of checking gas bills will testify. The responsibility for excessive bills is thus taken from the gas employees and thrown entirely upon the gas-registering mechanism itself. Those people, then, who chuckle furtively over the fact that the gas company has not ‘caught on’ to the surreptitious use of gas ranges are either the fortunate possessors of ‘slow’ meters or are deluding themselves as to the amount of gas which they actually consume. [Illustration: FIG. 4.--INTERIOR OF COMMON GAS METER.]