I know what the formula was supposed to do:

=SumEvalString($C3:INDEX($C3:CN3,MATCH(Base_Year,$ C$1:$CN$1,-1)))

This looks at all cells between $C3 and Base_year (which happens to be
cell $B$35).

Those cells would have a format of '12-5
or '12-5:1:2
or '12-5:1:2:C

The calculation for each cell would be
(5 - 12)
or (12 - 5 + ($b$35 * 1) + ($b$36 * 2)
or (12 - 5 + ($b$35 * 1) + ($b$36 * 2) + $b$37


I suspect my macro is gone, so I would need to:
1. Recreate it.
2. Find out how it disappeared and make sure that doesn't happen
again.

--
"In no part of the constitution is more wisdom to be found,
than in the clause which confides the question of war or peace
to the legislature, and not to the executive department."

- James Madison