LOOKUP function problem?
 

I have a data sheet from A3:F59. I input a number in G12. G12 is a number
with one decimal point. I need to look up G12 in the collumn F3:F59 and find
the exact or closest number to G12 and then go accross that row to the first
column and read out that cell on A3:A59. The numbers in the column F3:F59 are
in 2 decimal points and in ascending order. I used the formula:
LOOKUP(G12,F3:F59,A3:A59)

For some numbers, it works fine but if the G12 falls between 2 numbers on
F3:F59, it returns the cell above the closest number. I tried both vector and
array formats for LOOKUP but no results. How can I fix this problem as I need
to get the cell which is the closest to the value of numbers in F3:F59?
Thanks for your help.
Dori