These questions are more out of curiosity than anything else.  I have
been experimenting with VLOOKUP with an exact match, and would like
some background to what seems to me to be curious behaviour.

In cells A1:A4 I have

0.1
0.5
=1/3
0.4

The =1/3 displays as 0.333333333 in the cell and as =1/3 in the
formula bar.

In C1 I have: =VLOOKUP(D1,A1:A4,1,FALSE)

In E1 I have =D1-A3, formatted as scientific with 2 decimal places.

If I enter =1/3 in cell D1 I get a match and E1 displays 0.00E+00, as
expected.

Now for the curious bits.

If I enter 0.333333333333333 in D1 (15 3's) then E1 knows this is as
close to 1/3 as you can get with the available precision, and displays
0.00E+00, but VLOOKUP doesn't seem to know this and displays #N/A.

If I enter +1/3 this displays as 0.333333333333333 in the formula bar,
but I get a match.

If I now press F2-enter the display in the formula bar doesn't change,
but the VLOOKUP gives #N/A.  E1 still displays 0.00E+00.

All this is with XL2007.

My questions are:

Why does entering +1/3 convert itself into 0.333333333333333 in the
formula bar, but =1/3 doesn't?

Why does the value used in the VLOOKUP continue to be 1/3 until I
press F2-enter?

If subtracting two very close (but not exactly equal) numbers results
in a display of exactly zero, why doesn't VLOOKUP work the same way?

Is there a lookup or match function that allows me to specify a
precision for an exact match, or do I have to write my own?