Where it is not practicable to compute the annual gross volume of
sales or business under paragraph (b) of Sec. 779.266 in time to
determine obligations under the Act for the current quarter, an
enterprise or establishment may use a 1-month grace period. If this 1-
month grace period is used, the computations made under this section
will determine its obligations under the Act for the 3-month period
commencing 1 month after the end of the preceding calendar or fiscal
quarter. Once adopted the same basis must be used for each successive 3-
month period.