Ahh, a question I'd never thought to ask. Am a bit surprised such a thing can still be had at all. Still have instructions to some smaller sheets sold via a model RR supplier in 1980s and hadn't seen much of anything available since.
later, Forrest Today's scientists have substituted mathematics for experiments, and they wander off through equation after equation, and eventually build a structure which has no relation to reality. -- Nikola Tesla, July, 1934