If condition problem

Hi all, I am building a code that does a similar job like MATCH INDEX or Vlookup.
but these functions need their inputs to be in an certain order if i want a APPROX match.
so I built my own code.
I worked for a while and now it doesn't anymore...

here is my condition that gives me headache

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I am debugging it, so there might be some wierd stuff and stuff that are commented. but the real headache part is here:

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first and second statement works fine, at the third, it doesn't here is sample result:

622 621
622 622
165 622
165 165
165 165
168 165
170 168

(these are j value, for loop iteration, or row number)

Some BG story.
Its a code to approximate a Milepost depending on the GPS location. the mile post has been approximated depeding on the distance different points has. but the data acquisition is every 10 seconds. so there are holes and we want a more "accurate" approx. so I built something that gets the two closest points (over and under the searching value). after i simply extrapolate the value and search it via the wanted value. the prob is j is not comparing properly..

thank you all!

Well I think I sort of solved the problem by adding a new variable instead of rowafter and rowbefore.

But I still have a problem with the comparison with the doubles.
I tried to round them to 10 decimals, but it seems like it doesn't work.
any help?

here is the updated code :

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