| Name | London Name Plate Mark 4 Ref no. 6B / 490 Navigational Computer Dead Reckoning |
| Front Scales | C = D 1) = 2) = 3) = 4) |
| Back Scales | 5) = 6) |
| Type of Rule | disc(s) |
| Material | metal |
| Dimension (mm) | 282x125x6 |
| Area of Use | aviation |
| Origin of Rule | Herman van Herwijnen |
| Match Number | 1742 |
| Comment | |
| Thumbnail |  |