| Year | 1920 |
| Date | 25-Nov |
| Volume | 43 |
| Issue | 1,022 |
| Page | 423 |
| Category | Electrical |
| Part | |
| Title | Making a "P.O." Resistance Box |
| Author | A.V.Ballhatchet |
| Notes | The resistances, the plug blocks, the tapping keys, assembling, principles and use, theoretical diagram of Wheatstone bridge |