| Subject | English | German |
| radiat. | reference direction | Referenzrichtung (of an X-ray tube) |
| opt. | reference direction | Bezugsrichtung (e.g. in space) |
| life.sc. | reference direction | Nullrichtung |
| earth.sc., tech. | reference direction | Referenzrichtung |
| phys. | reference direction | Bezugsrichtung |
| radiat. | reference direction | Bezugsrichtung (of an X-ray tube) |
| earth.sc., tech. | source reference direction | Referenzrichtung |