This is clearly abook which is standardized.
He knows for certain that his page 534 will exactly agree with my page 534."
"But very few books would correspond with that."
"Exactly. Therein lies our salvation. Our search is narrowed down to standardized books which anyone may be supposed to possess."
"Bradshaw!"
"There are difficulties, Watson. The vocabulary of Bradshaw is nervous and terse, but limited. The selection of words would hardly lend itself to the sending of general messages. We will eliminate Bradshaw. The dictionary is, I fear, inadmissible for the same reason. What then is left?"
"An almanac!"
"Excellent, Watson! I am very much mistaken if you have not touched the spot.
An almanac! Let us consider the claims of Whitaker's Almanac.
It is in common use.