A simpler explanation is offered in FL Bauer's "Decrypted Secrets - Methods and maximis in cryptology" IBSN: 3-540-66871-3
However, polyphonic ciphers were used in the ancient civilisations betwen the Nile and the Euphrates. As the letters of the alphabet also served as number symbols, it was a popular pastime to add up the values of the symbols representing a secret word (gematria). In this way the isopsephon 666 mentioned in the Aplocalypse (Rev. 13.18) has been taken to represent the Emperor Nero (Fig 20). There are said to be people who refuse to accept a car registration involving the "number of the beast" 666.
The figure referred to (Fig 20) is difficult to reproduce here in text, however I will do my best...
Nun Vav Resh Nun Resh Samex Koph
50 6 200 50 200 60 100
N O Re N Ra Sæ C
When spelt out right-to-left (as
Hebrew text is read) Koph-Samex-Resh Nun-Resh-Vav-Nun, 100-60-200 50-200-6-50, C
aeS
aR N
eRON (yes, Neron - not Nero - is correct) we get our 666. Some support
for this theory comes from the fact that the latin verson "CAESAR NERO" equals 616 - a number found in some bibical texts, and the
Hebrew version "CAESAR NERON" equals 666.