A view of the dials of a modern electric meter is given in Fig. 43. The method of reading is similar to that for the dials of a gas meter as explained on page 144. The reading in Fig. 43 is 538 kilowatt hours. In taking down these figures one should read the dials from right to left; that is, in the reverse of the usual order of writing numbers. The pointer on the dial at the extreme right points to 8; the number 8 is written down as the figure in the units place. The index of the next dial to the left has passed the 3, but has not reached the 4, as shown by the fact that the units' dial reads 8; the figure 3 is accordingly written in the tens' place. The index of the third dial has passed the 5, and this figure is to be written in the hundreds' place, giving 538 kilowatt hours as the reading of the meter, since the index of the dial at the extreme left has not reached the figure 1. If the index hand of the second dial in Fig. 43 be turned slightly so as to point to, or even slightly past, the figure 4, it becomes more difficult to read the meter correctly, as a hasty inspection may result in the reading being made as 548 kilowatt hours. However, the index of the units' dial standing on the figure 8 shows that it has not quite completed a revolution, and hence that the index of the second dial (if it is properly-set on its shaft) should be close to a division and about to reach it. Hence, it should be read as having passed the 3 and not having reached the 4. A view of a meter dial face having the second index to the left slightly displaced in this way is shown in Fig. 44.

Kilowatt Hours

Fig. 43. - Dial of a watthour meter. In this dial the hands are correctly set on their shafts. The reading is 538 kilowatt hours.

Kilowatt Hours

Fig. 44. - Dial of a watthour meter. In this dial the hand on the second circle from the right is slightly in advance of its proper position on its shaft. The reading is the same as in Fig. 43, namely, 538 kilowatt hours, although at a glance it might be incorrectly read as 548 kilowatt hours.

When one dial hand points to 9, special care must be taken that the dial hand of the next higher dial is not read too high, as it may appear to have reached the next number, but will not have done so until the dial hand at 9 has come to 0. A simple illustration will make this clear. If the hour hand of a clock points to 10, as closely as can be read, and if the clock had no minute hand, the time would be read as 10 o'clock. If the minute hand, however, is pointing to the figure 11, the time is read as 9.55. Ten minutes later the hour hand may not have moved perceptibly, but the time is now read as 10.05. Similarly, in the electric meter, the reading of each dial must be interpreted by noting the reading of the next dial to the right.

The dial hands on adjacent dials revolve in opposite directions; therefore, a reading should always be checked after being written down, as it is easy to mistake the direction of rotation.