The last digit on the right is always a “zero” and is a fixed digit stamped on the face of the meter. It is not read and does not change.
The 2nd from the right dial measure 'tens' and is also not read since we bill in hundred gallons. It does turn, and when it reaches '9', it becomes a zero again and the third digit from the right advances to the next number.
The 3rd, 4th, 5th, and 6th from right dial measures “hundreds”, “thousands”, “ten thousands”, and “hundred thousands” respectively and advances each time the previous dial on the right reaches “9” and turns to “0”
(Some larger commercial meters may have more fixed zeros)
The gallons used are calculated by subtracting the previous month's reading from the current reading.
For example:
00245.40 Reading is 245
30 days later :
00324.10 Reading is 324
Current reading 324, previous reading 245, Usage 79 (7,900) gallons