finding the middle cell in a column of numbers

Hi Guys,

Not sure of the right tiltle here goes

I am looking for a formulas to first find the middle number in a column of numbers eg 1,2,3,4,5 3 is the middle (similar to median) thats where the calculations start...

it then assigns values of minus to the numbers above the middle and plus values to the numbers below the middle
1 -50
2 -50
3 0
4 +50
5 +50




now when it comes to even numbers eg 1,2,3,4,5,6 if i use median it divide 3 & 4 and comes up with 3.5 ........ i want it to recognize 3 and 4 as the middle numbers
and assign plus and minuses above and below the middle numbers
1 -50
2 -50
3 -25
4 +25
5 +50
6 + 50

I do hope you all understand, this has been buggin me for weeks

cheers in advance