Assuming first column is data and second expected result:

for data of #NUM! will fail (error) on the "A1=0" (non-numeric) test while
for A1=0, your test returns zero (not div/0). Your test will only work for A1
being a non-zero valid number. (I assume b0 is a typo).

Why should they be 9.419?

"bastien86" wrote:

I have the data

0.102365034 9.419
#NUM! #NUM!
0 div/0

I put the formula in:

=IF(OR(A1=0,ISERROR(A1)),b0,1/a1-1/2.86)

for the column on the right and filled down. How come my 2nd and 3rd lines
on the right column aren't 9.419