| Year | 1937 |
| Date | 05-Aug |
| Volume | 77 |
| Issue | 1,891 |
| Page | 141 |
| Category | Workshop |
| Part | |
| Title | A Change-Wheel Problem |
| Author | Geo. Gentry |
| Notes | The problem according to the querist, our idea of the question, the arithmetical explanation, first reference to a compound train, some other compound trains |