For the purpose of effectively applying the provisions of this classification of operating expenses to the accounts of all companies, such companies are divided into two classes, as follows:
Class A. Companies having annual operating revenues of $1,000,000 or more.
Class B. Companies having annual operating revenues of less than $1,000,000.
All companies will keep Balance Sheet, Utility Plant, Income, Surplus and Operating Revenue accounts as provided in this system of accounts (so far as applicable to their business).
The class to which any utility belongs shall originally be determined by the average of its annual gas operating revenues for the last three consecutive years. Subsequent changes in classification shall be made when the annual gas operating revenues for each of the three immediately preceding years shall exceed the upper limit, or be less than the lower limit, of the annual gas operating revenues of the classification previously applicable to the utility.
Any utility may, at its option, adopt the system of accounts prescribed by the Department for the next larger class.
220 CMR, 50, 5