Hi everyone, really need help right here.
i've try and make some alteration of the coding to calculate the distance between latitude and longitude from http://www.cpearson.com/excel/latlong.htm with the help from other excel forum user. The coding is as below :

Option Explicit

Private Const C_RADIUS_EARTH_KM As Double = 6371.1
Private Const C_PI As Double = 3.14159265358979

Function GreatCircleDistance(Latitude1 As Double, Longitude1 As Double, _
Latitude2 As Double, Longitude2 As Double) As Double

Dim Lat1 As Double
Dim Lat2 As Double
Dim long1 As Double
Dim long2 As Double
Dim X As Long
Dim Delta As Double

X = 24

' convert to decimal degrees
Lat1 = Latitude1 * X
long1 = Longitude1 * X
Lat2 = Latitude2 * X
long2 = Longitude2 * X

' convert to radians: radians = (degrees/180) * PI
Lat1 = (Lat1 / 180) * C_PI
Lat2 = (Lat2 / 180) * C_PI
long1 = (long1 / 180) * C_PI
long2 = (long2 / 180) * C_PI

' get the central spherical angle
Delta = ((2 * ArcSin(Sqr((Sin((Lat1 - Lat2) / 2) ^ 2) + _
Cos(Lat1) * Cos(Lat2) * (Sin((long1 - long2) / 2) ^ 2)))))

GreatCircleDistance = Delta * C_RADIUS_EARTH_KM

End Function

Function ArcSin(X As Double) As Double
' VBA doesn't have an ArcSin function. Improvise
ArcSin = Atn(X / Sqr(-X * X + 1))
End Function

Sub Checking()

    Dim i As Long
    Dim Lat1 As Double
    Dim long1 As Double
    Dim Lat2 As Double
    Dim long2 As Double
    
    Application.ScreenUpdating = False
    
    i = 4
    Do While Not IsEmpty(Cells(i, 1))
        Lat1 = Cells(i, 1)
        long1 = Cells(i, 2)
        Lat2 = Cells(i, 3)
        long2 = Cells(i, 4)
        
        Cells(i, 5) = GreatCircleDistance(Lat1, long1, Lat2, long2)
        
        i = i + 1
    Loop
    
    Application.ScreenUpdating = True

End Sub
However, when i try to run the macro, it turn to have
compile error:
Argument not optional

i think it because of the

Cells(i, 5) = GreatCircleDistance(Lat1, long1, Lat2, long2)

does not declare all argument from the GreatCicrcleDistance function. but when i put all the arguments to the equation, nothing is happen.

Actually how to apply the function so it can be use in the excel sheet.?

Thank you very much in advance.