VLOOKUP (VERT.ZOEKEN) in Excel sometimes returns wrong value (off by one row)

Ever had that the Excel formula VLOOKUP start coming up with the wrong answer? Trouble is that most times it has the correct answer, but sometimes it doesn’t.

I found the answer on the internet, see below:

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Sounds like you are using no range lookup value

=vlookup(lookup_value,table,column_index_range_loo kup)

=vlookup(a1,b2:c50,2,false)

if you don’t use false (or zero) it will need the leftmost column sorted in
ascending order
and false also makes it look for the exact value and will return an error
otherwise but leaving it out or using true will lookup the largest value
less than or equal to the lookup value
—

Regards,
Peo Sjoblom

Taken from http://www.excelbanter.com/showthread.php?t=194717