Function RND() As Variant
' Implements Excel's RAND() algorithm with full control of the seed.
'
' http://support.microsoft.com/kb/828795
'
' C IX, IY, IZ SHOULD BE SET TO INTEGER VALUES BETWEEN 1 AND 30000 BEFORE FIRST ENTRY
' IX = MOD(171 * IX, 30269)
' IY = MOD(172 * IY, 30307)
' IZ = MOD(170 * IZ, 30323)
' RANDOM = AMOD(FLOAT(IX) / 30269.0 + FLOAT(IY) / 30307.0 + FLOAT(IZ) / 30323.0, 1.0)
'
    Dim Xi      As Long
    Dim Yi      As Long
    Dim Zi      As Long
    Dim LAST_X  As Long
    Dim LAST_Y  As Long
    Dim LAST_Z  As Long
    
    LAST_X = Range("last_x").Value
    LAST_Y = Range("last_y").Value
    LAST_Z = Range("last_z").Value
    
    If LAST_X = 0 Or LAST_Y = 0 Or LAST_Z = 0 Then
        LAST_X = Range("seed_x").Value
        LAST_Y = Range("seed_y").Value
        LAST_Z = Range("seed_z").Value
    End If
    
    Xi = (171 * LAST_X) Mod 30269
    Yi = (172 * LAST_Y) Mod 30307
    Zi = (170 * LAST_Z) Mod 30323
   
    Range("last_x").Value = Xi ' F8 goes back to top when function dimmed as Variant
    Range("last_y").Value = Yi
    Range("last_z").Value = Zi
    
    RND = (Xi / 30269 + Yi / 30307 + Zi / 30323) - Int(Xi / 30269 + Yi / 30307 + Zi / 30323)
       
End Function