Here is a little sample from a very large worksheet. The first column
contains values which I want to use in a calculation, and the second column
index values representing coordinates of a location.

3435.3 350,50
3999 350,50
1884.7 400,50
1942.4 400,50
2156.7 400,50
2259.7 400,50
2403.9 400,50
3601.6 400,50
3710.3 400,50
3999 400,50
2004.8 100,200
2031.1 100,200
2057.4 100,200

I can easily use MATCH to find the first row which has the index 400,50, but
how can I use it to determine the last row which has this value? The values
are not sorted in any order so it wouldn't be possible to predict the value
of the index following 400.50. Is there a MATCH which will search up from the
bottom of the worksheet? How could I incorporate some test to check whether
the value of this index is the same or different on the following row?

Grateful for advice.