Compare Cell against previous cell

[GRE86]

Hi all, need some help.

I have a list of depths within one column ("I"), the top of that column (I12) contains the word "depth". I need a script that will compare the 2nd depth (I14) to the 1st (I13) to make sure its deeper (larger value), then 3rd (I15) to 2nd (I14), 4th (I16) to 3rd (I15), 5th (I17) to 4th (I16) and so on. Basically a script that will make sure the previous value is less than the next value.

I also need the script to:

Ignore the depth row (I12)
ignore blanks (after the last data point)
and this is not a static list, the length of the list can vary depend on number of data points.

I have used the color scale conditional formatting but the colour changes are too acute to recognise. I also =OFFSET(INDIRECT(ADDRESS(ROW(), COLUMN())),-1,0) but this will attempted to compare the first depth point to the word "depth" and also the last data point to a blank cell.

any help would be appreciated

 

[GRE86]

Update:

Managed to get it to work with conditional formatting but would prefer the error message prompt. So far i have:

Private Sub Worksheet_Change(ByVal Target As Range)
For I = 13 To 999
If Cells(I, "I") > Cells(I + 1, "I") Then
x = 1
Cells(I, "I").Select
Exit For
End If
Next I


If x = 1 Then MsgBox "Error"


End Sub

Unfortunately, this script is giving an error messages as the last value in the list is greater than the blank cell below it, any improvements would be appreciated