Even though they are simple they can be very puzzling indeed. Now suppose that you write the letter from the bottom line each time you mean a letter on the top line.
The person finds the word "darkness", which happens to be the seventh word on the fifteenth line on page two hundred and forty-one. Nevertheless, skilled cryptographers can work out messages written even in this complicated way. Look for three letter words that are used often.
Without a decoding program such as this one, the code solver must use some ingenuity. The next time an "a" is needed a different page and word will be used, so that no-one can see a pattern in the coded text.
They are quite likely to be "the" or "and". This sort of code must be rather boring to write and frustrating to decode.
Because it's too easy to decode. There are only two in every-day English, "I" and "a". Book Codes Book codes are much harder to crack, because there is no logical order in the encoded material.
Backwards Alphabet Code. I picked the number 3.