Hello Mark,

Why OFFSET? Take INDEX:
=SLOPE(INDEX(A2:G2,1,LOOKUP(2,1/ISERROR(A2:G2),{1,2,3,4,5,6,7})
+1):G2,INDEX($E$1:$K$1,1,LOOKUP(2,1/ISERROR(A2:G2),{1,2,3,4,5,6,7})+1):
$K$1)
It's not volatile.

Regards,
Bernd