Объясните, пожалуйста, суть кода

Sub O_pricing1()
 
Dim x1 As Double, x2 As Double
Dim n1 As Double, n2 As Double
Dim i As Long, j As Long
Dim n As Integer
Dim start1 As Integer
Dim sum As Double, sumvar As Double
Dim estimate As Double, Ex As Double, Varn As Double
Dim correct As Double
Dim S0 As Double, Strike As Double, r As Double
Dim sigma As Double, T As Double
Dim hilf1 As Double, hilf2 As Double, hilf3 As Double
Dim hilf4 As Double
Dim mu3 As Double, sigma3 As Double
 
 
Rnd (-1)
start1 = Worksheets("O_Pricing1").Range("A9").Value
Randomize (start1)
mu3 = 0
sigma3 = 1
 
S0 = Worksheets("O_Pricing1").Range("A11").Value
Strike = Worksheets("O_Pricing1").Range("A13").Value
r = Worksheets("O_Pricing1").Range("A15").Value
sigma = Worksheets("O_Pricing1").Range("A17").Value
T = Worksheets("O_Pricing1").Range("A19").Value
 
'Black-Scholes formula
hilf1 = (Log(S0 / Strike) + (r + 0.5 * sigma * sigma) * T) / (sigma * Sqr(T))
hilf2 = hilf1 - sigma * Sqr(T)
hilf3 = Application.WorksheetFunction.NormSDist(hilf1)
hilf4 = Application.WorksheetFunction.NormSDist(hilf2)
 
correct = S0 * hilf3 - Strike * Exp(-r * T) * hilf4
    Worksheets("O_Pricing1").Cells(5, 8) = correct
    Worksheets("O_Pricing1").Cells(6, 8) = correct
    Worksheets("O_Pricing1").Cells(7, 8) = correct
    Worksheets("O_Pricing1").Cells(8, 8) = correct
    Worksheets("O_Pricing1").Cells(9, 8) = correct
 
'preparations for the loop
hilf3 = S0 * Exp((r - 0.5 * sigma * sigma) * T)
hilf4 = Sqr(T)
 
For i = 1 To 5
 
j = Worksheets("O_Pricing1").Cells(i + 4, 4)
If (j < 4) Or (j > 30000) Then
    j = 4
    Worksheets("O_Pricing1").Cells(i + 4, 4) = j
End If
If (j Mod 2 = 1) Then
    j = j + 1
    Worksheets("O_Pricing1").Cells(i + 4, 4) = j
End If
n = j / 2
 
sum = 0
sumvar = 0
 
    For j = 1 To n
        x1 = Rnd
        x2 = Rnd
        n1 = Application.WorksheetFunction.NormInv(x1, mu3, sigma3)
        n2 = Application.WorksheetFunction.NormInv(x2, mu3, sigma3)
        
        'Calculate stock price in T
        hilf1 = hilf3 * Exp(sigma * hilf4 * n1)
        hilf2 = hilf3 * Exp(sigma * hilf4 * n2)
        'Calculate payoff
        If hilf1 > Strike Then hilf1 = hilf1 - Strike Else hilf1 = 0
        If hilf2 > Strike Then hilf2 = hilf2 - Strike Else hilf2 = 0
                
        sum = sum + hilf1 + hilf2
        sumvar = sumvar + hilf1 * hilf1 + hilf2 * hilf2
    Next j
    
Ex = sum / (2 * n)
estimate = Exp(-r * T) * Ex
 
Varn = (sumvar / (2 * n) - Ex * Ex) / (2 * n - 1)
Varn = Sqr(Exp(-r * T * 2) * Varn)
 
    Worksheets("O_Pricing1").Cells(i + 4, 5) = estimate
    If (estimate - 1.96 * Varn) < 0 Then
        Worksheets("O_Pricing1").Cells(i + 4, 6) = 0
        Else
        Worksheets("O_Pricing1").Cells(i + 4, 6) = estimate - 1.96 * Varn
    End If
    Worksheets("O_Pricing1").Cells(i + 4, 7) = estimate + 1.96 * Varn
Next i
 
End Sub