Isnumeric Function - Getting Range To Extend By 1 If Not Numeric

So I found a great piece of code which calculates relative strength index. However, I've been trying to edit it to make it a bit more dynamic and I'm really struggling to get it to work.

Right now the initial code is:

Code:
Function RSI(MyCells As Range)
Dim up_day, down_day
Dim average_up, average_down
Dim RS, cellcount As Long
Dim cll As Rangeups = 0up_day = 0downs = 0down_day = 0cellcount = 0For Each cll In MyCells

[Code] ..........

Basically I tried to amend this as follows:

Code:
Function RSE(MyCells As Range, Length As Double)Dim up_day, down_day, ups, downs
Dim average_up, average_down
Dim rs, cellcount, rangecount As Long
Dim cll As Range
ups = 0

[Code] ..........

Basically i wanted it to look at the numbers in the range and then error check to see if it was a number... if it was a number great. If not then the length of numbers it should calculate across should increase by 1 as it has to include another number to calc across (hope this makes sense). however, i just cant get it to work at all. My code doesn't seem to make any difference. And it also raises the issue of the fact that the intial value for length also needs to be stored to do the final calc.