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I have just read the latest two postings.  I was about to post the following but it seems the date has now been determined.

Nonetheless I will post as it provides a little additional background.

I believe that this sextant is the Mark “A” “Nubel” Bell Sextant.  I attach an advertisement from 1951.  If the specification fits, I think you have identified the correct model.

here is what I was about to post - I have left it unchanged...

In terms of refining the date of manufacture I have some thoughts.  I have some other observations irrelevant to the date, but perhaps of interest.

Firstly, in the first photo you uploaded (September 4^th) it appears that there is an outline of the original certificate, including screw holes, to the left and right of the 1969 certificate.  Others have already noted that the sextant is older than 1969, and I don’t think that is in any doubt.  But this small detail further confirms that the certificate is not original.

The sextant is fitted with the Hezzanith Endless Tangent Screw, as opposed to essentially the same piece of kit but badged as the Hezzanith Endless Rapid Reader.  You will note that in the 1951 advertisement the sextant is described as fitted with the Rapid Reader.  I believe  - but need the primary source evidence – that the Endless Rapid Reader replaced the Endless Tangent Screw.  I can provide detailed photographs of the Rapid Reader on my Heath & Co. sextant (1957) for comparison if interested.

I do know this – though it is weaker evidence than I would like.  There are images online of the Endless Tangent Screw on pre-war sextants.  For example – see here:

https://www.antiquesofthesea.com/3990_Heath_Sextant.html

I also know that there are photos online from soon after the war with the Endless Rapid Reader.

The micrometer drum on the Sextant you have is newer than that in the link above.  Check out this excellent image of a different model from Heath & Co. but with the Endless Tangent Screw.  Note the micrometer drum.  This dates from 1935.  I believe yours is newer – possibly late 30s as I have seen wartime Heath & Co sextants with the newer micrometer drum.

https://collections.museumsvictoria.com.au/items/400366

And this – from 1946 – which is a three-circle sextant but with the Endless Tangent Screw I believe the same as yours.  See the micrometer drum.

https://www.skinnerinc.com/auctions/2857M/lots/426

By 1949 the Heath & Co. sextants had the Rapid Reader.  But I don’t know if there was a period of time when the two crossed over.

So my best guess is wartime through to 1949.

There will be something engraved on the lower arc under the index arm.  This is obscured in your photos.  It will probably just be the following: “Heath & Co New Eltham London S.E.9.”  But the engraving further aids comparison with sextants of the same age.

Murray.

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