It consists of nearly 6,000 primitive words, exclusive of the inflexions of verbs, &c., making in all upwards of 30,000 real words; the sentences have also been extended to about 6,000, with 1,500 syllables, a Geographical Table, a Table of Technical Terms, a Table of Stores and Provisions, and a Spare Table for Local Significations.
With so large a number of signals the limitation in the number of flags that can be conveniently hoisted at a time made itself at once felt, and Popham found himself compelled to abandon the "simple numerary" method. Taking the limit of convenience at three flags, the ten numeral flags of the Admiralty Signal Book would suffice for only 999 signals. Popham, therefore, after calculating the number of combinations available with various sets of flags, chose 23. These, which were mostly of his own design, he denoted by the numbers 1 to 9 and the letters A to O. With these 23 flags the number of available combinations is as follows:
| Singly | 23 | |
| Two at a time | 506 | |
| Three at a time | 10,626 | |
| ——— | ||
| Total | 11,155 |
So that upwards of 11,000 signals could be made using no more than three flags in one hoist.
Hoisting four flags at a time, the number of possible signals with 23 flags is increased by 212,520, making 223,675 in all, sufficient for the most exhaustive vocabulary. If this code had been invented seven years earlier, Nelson could have made his signal in precisely his own words, the first three of which would have been as follows: England, 69B; confides, 5I3; that, B67. Curiously enough, Popham, in 1812, seems to have preferred "confides" to "expects," for the former was one of "most needed" words and could be made by three flags, whereas "expects" was No. 6138 and required four.
In demonstrating the extensive use to which his code could be put, Popham gives one or two amusing illustrations, apparently in all seriousness. Thus:
| FA1 | Have you an idea |
| G647 | a change of ministers is about to take place |
| 52A | Certainly |
| 8BF | not |
| G643 | ministers are gaining strength |
| BOE | Your |
| AC8 | sister |
| 852 | married |
| 85F | to |
| C87 | a Lord of the Admiralty |
This vocabulary, published in 1812, was such an evident improvement that it was issued to the fleet in 1813.
In 1816 it was revised by Popham and re-issued by the Admiralty as an official Vocabulary Signal Book. Eleven years later the signal books were again revised and re-cast in three volumes:—