I would like to introduce you to what could be the longest excel formula in the world. It likes long walks on the beach, summing, counting, offsetting, matching, indirect functions, if statements, row functions and probably more if I reread it, which I will never do again. Do not get to close or it will consume you as it did me.
=SUMIFS(OFFSET(INDIRECT("H"& MATCH('Line
Targets'!B1,B8:B91,0)+ROW(B8),TRUE),IF(ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0)))<10,-ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0))),-10),0,IF(ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0)))<10,ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0))),10),1),OFFSET(INDIRECT("B"& MATCH('Line
Targets'!B1,B8:B91,0)+ROW(B8),TRUE),-IF(ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0)))<10,ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0))),10),0,IF(ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0)))<10,ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0))),10),1),"<="&'Line
Targets'!$B$1)/COUNTIFS(OFFSET(INDIRECT("B"& MATCH('Line
Targets'!B1,B8:B91,0)+ROW(B8),TRUE),-IF(ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0)))<10,ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0))),10),0,IF(ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0)))<10,ROW( INDIRECT("b"& MATCH('Line
Targets'!B1,B8:B91,0))),10),1),"<="&'Line Targets'!$B$1)
signed,
a broken man