| Name and Model Number | Aristo 920 Federfix |
| Country of Origin | Germany |
| Date of Manufacture | |
| Front Scales | Many specialised scales and curves |
| Back Scales | None |
| Scale Length | 34.6 cm maximum |
| Type of Rule | Instrument |
| Construction | Plastic |
| Area of Use | Technical |
| Comment | Used in the computation for cylindrical coiled springs. |
| Rarity | RRR |
| Donor | Collection of Rod Lovett |
| Match Number | 9 |
| Thumbnail |  |
| RR | = Rare -- 1 of 25 collectors has one; it may take a year to find an example in the marketplace. |
| RRR | = Very rare -- only very few known to collectors; may take several years before one comes up for sale. |
| RRRR | = Extremely rare -- a museum piece; unlikely that an example will ever come up for sale. |