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Earlier I happened across What's the small white gadget with two black buttons in this video of the International Space Station? via the HNQ list. I was intrigued by the snippet from the "International Space Station Expedition Crew Training Notebook" posted in the answer by Organic Marble, which says:

Located on the "right hand" side as you enter any US Module with feet pointing nadir (1g ref).

I understand the use of zenith and nadir in this context (although it amused me that you have to say which way your feet are pointing, that would not have occurred to me!).

I don't understand the "(1g ref)". Surely the nadir is still the nadir (the side that points towards earth / "down" in the local gravitational field), regardless of the strength of the gravitational force, and indeed surely there is much less than 1g acting on the ISS towards earth, assuming the interpretation of "1g" to mean "9.8 m/s^2".

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  • $\begingroup$ Good question! That is the only time the phrase "1g ref" appears in the document. I think the meaning is clear - as you say, the purpose is to define which way is "right" - so I think it's just an infelicity in the writing. I'll see if "1g ref" appears anywhere else. $\endgroup$ May 22 at 20:38
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    $\begingroup$ Related: space.stackexchange.com/q/19727/6944 Note on the ISS, the side of the station named "nadir" does not have to point down (although it usually does). $\endgroup$ May 22 at 20:55
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    $\begingroup$ @OrganicMarble Thank you... if you make this into an answer I can upvote / accept... $\endgroup$
    – Vicky
    May 23 at 11:22

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