I tried this:
=AVERAGE(INDIRECT("D"&(8+$AJ$7*$AJ9)&":D"&(8+$AJ$7 *$AJ9+$AJ$7-1)))
where D8 is the first of the long column of data, and ak8 through a
large number contains the compressed averages, while aj8 and up count
the instances, starting with 0 in aj8. AJ7 contains the divider. Your
method is much more elegant. Thanks!

T. Valko wrote:
Typo:


C1 = 10
=AVERAGE(OFFSET(A$1,(ROWS(B$1:B1)-1)*C$1,,10))


Should be:

=AVERAGE(OFFSET(A$1,(ROWS(B$1:B1)-1)*C$1,,C$1))