Glad to be able to help Radka.
Just one last thing...If you use option Explicit, the original mis-spelling I pointed out will be picked up by Excel and you will be told you have an undeclared variable, i.e.
Option Explicit
Sub Voltage()
Dim Voltage, Difference As Variant
Dim i As Integer, AvrPoints As Boolean
Dim LastRow As Long
AvrPoints = False
ActiveCell.Offset(0, 1).Select
LastRow = ActiveSheet.Range("B65536").End(xlUp).Row
Do Until AvrPoints = True
For i = 1 To LastRow
Voltage = Application.WorksheetFunction.Average(ActiveSheet.Range("B1:B" & i))
Difference = Cells(i + 1, 2) - Voltage
If Difference > 0.0004 Then
AvrPoints = True
End If
Next i
Loop
MsgBox Voltage
End Sub
John