NavList:

Geoffrey, of the Astra reproduction with the inadequate shades, you asked:
"Would you go further, Frank, and say that this sextant is therefore dangerous? Do we have a moral duty to inform ebay that they are selling a device which could blind if used in the manner in which it is obviously intended?"

Well, I wouldn't. That strikes me as a slippery slope. Ebay might just ban all sextant sales (and this sounds vaguely familiar, so maybe that's why you brought it up?). Besides, the reason people don't look at the Sun and blind themselves is instinct. If a would-be navigator aimed this "sextant" at the Sun, they would immediately look away by instinct. Every corner store sells "sunglasses" which reduce the brightness of the Sun somewhat, but we don't feel any need to warn people not to look at the Sun while wearing them.

And you wrote:
"I have actually used an Indian reproduction sextant of the sort that was meant for "hanging on the wall in a restaurant". The shades on that particular 'instrument' were actually pretty good, and even though the scale precision was only one degree, I recall that the resulting fix was not too bad either."

Yeah, as long as they have two decent mirrors perpendicular to a common plane, it's a true instrument of reflection, fully capable of measuring angles with an accuracy of at least a few minutes of arc. But the arc scale is "decorative" on these instruments, so the reading may be only loosely related to the actual angle. If an instrument like this is calibrated, the resulting arc error table could make it respectably accurate in practice. But that's a lot of work when you could get similar performance from an inexpensive plastic sextant straight out of the box.

You also wrote:
"This 'instrument' is not obviously meant for the restaurant wall, but targets the novitiate celestial navigator who is looking for a cheap-but-good sextant and who would not realise that the shades are not adequate or anything close to being adequate."

You've got me thinking now about the "target" market for this sextant. Rather than being decorative, maybe it's something more obvious ...and nefarious: a deliberate counterfeit intended for sale in the merchant marine market. There's big money in this and little oversight. They still buy lots of sextants because they're required to do so by regulation. As we know, the great majority of these sextants are never removed from their cases. So a counterfeit sextant modeled closely on the Astra design might sell fairly well in markets that don't worry much about counterfeits, and the fakes might never be detected. I suppose now we're going to have to look very closely at "Astra" sextants for sale from regions of the world where sellers can get away with this. At least ebay, and I would guess most other auction sites based in western countries, will take action to cancel sales and selling accounts if they're informed that counterfeit items are being offered for sale on their sites. Yet a new wrinkle in the sextant-buying marketplace...

-FER

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