Option Explicit
Dim Vol, Volflow, ibod, dt, konstant, residence, rate, eBOD, time, Mass, i, nMass, dbod, counter
Public Sub Calculate_Click()
residence = Vol / Volflow
i = 0
time = 0
Mass = ibod * Vol
Do While time < residence
If i <= 1 Then Mass = nMass
BOD = Mass / Vol
rate = konstant * eBOD
dbod = rate * dt
nMass = Mass - (dbod * Vol)
counter = 5
Sheet("Ouput").Range("C" & counter) = time
Sheet("Ouput").Range("D" & counter) = Mass
Sheet("Ouput").Range("E" & counter) = eBOD
Sheet("Ouput").Range("F" & counter) = rate
Sheet("Ouput").Range("G" & counter) = dbod
Sheet("Ouput").Range("H" & counter) = nMass
time = time + dt
i = i + 1
c = c + 1
Loop
End Sub