| Share | Phrase |
|---|
| 40.25% | visual [perception] observation |
| 17.00% | observation circuit |
| 11.05% | observation period |
| 5.78% | observation window |
| 4.73% | operation observation |
| 4.02% | observation counter |
| 3.89% | observation [location] base |
| 3.66% | perform observation [perform operation] |
| 3.36% | make observation [perform operation] |
| 3.09% | permit observation [perform operation] |
| 1.78% | chamber observation |
| 1.33% | observation means |