LOOK UP not returning N/A value when match is not found

[Claudio Costa]

Hi, I used a very simple LOOKUP formula (column F in "Riassunto D" sheet). My problem is that when a lookup value is not found the N/A value is returned only up to when the first lookup value is found, then it repeats the previous value returned up to the next lookup value found... is this correct?

How can I get N/A value (or FALSE or similar) everytime the lookup value is not found?

[#2]

I would not use LOOKUP, but instead a combination of INDEX and MATCH:
=INDEX(DiffD_MM!$E$2:$E$9,MATCH(A3,DiffD_MM!$I$2:$I$9,0))