Kempenfelt's system assigned each of sixteen flags to a page and then used a second flag to select one of sixteen entries. Two adjacent hoists therefore encoded 256 prepared meanings without requiring a unique flag for each order. A computer-programming analogy treats the compact pair of symbols as a way to retrieve a defined instruction. The analogy presents the signal book as an information system built from flags.
Chapter · 25:33-27:46
How Kempenfelt's two-flag signal code worked
Sixteen numbered flags become a 256-entry code by using one flag for the signal-book page and a second for the instruction on that page.