|Nelem = (NAXIS2 × NAXIS3 × ... × NAXISm),||(7.3)|
where Nelem is the number of elements in the data array in a group, m is the value of NAXIS, and the NAXISn represent the values associated with those keywords.
The first parameter of the first group shall appear in the first location of the first data record. The first element of each array shall immediately follow the last parameter associated with that group. The first parameter of any subsequent group shall immediately follow the last element of the array of the previous group. The arrays shall be organized internally in the same way as an ordinary primary data array. If the groups data do not fill the final record, the remainder of the record shall be filled with zero values in the same way as a primary data array (§4.3.2). If random groups records are present, there shall be no primary data array.