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Brad

If you want me to provide a reference to the actual phrase ‘harbour marker’ in the text, glossary, or index of a recognised nautical book, I’m afraid the answer is “Still looking”.   ‘Harbour mark’ used with respect to compass adjustment is easy enough.  It appears in the index of the 1904 edition of the 'Wrinkles', and the method is described from pages 616-620.  I was fortunate to witness a compass adjuster using a method very similar to this in the 72ft ketch Spirit of Boadicea in 1991 except we motored the vessel’s head around rather than waiting for the tide to turn her.

The phrase ‘harbour marker’ used with respect to calculating chronometer error using sextant observations has so far come up blank.  The ‘Wrinkles’ and 'Nicholl’s Concise Guide – Vol II, 1933’ both describe the method, and ‘The Admiralty Navigation Manual – Vol III 1938’ describes several methods at length.  All have worked examples starting with a known lat and long to the nearest second of arc, but unfortunately they don’t say where they got it from, probably from tables or the chart. 

Therefore, we’re left with searching Google.  First to come up are harbour approaches.  This is a rather nice one: Porthgain Harbour https://www.stayinwales.co.uk/wales_picture.cfm?p=3750 .  I can’t check if the phrase ‘harbour marker’ appears in any of my pilot books, because they’re all aboard TIKI in Brough Haven.  Then there are the disc markers like this one: Irvine Harbour Point Marker https://www.flickr.com/photos/gordonjc/4416887581 , but most of these appear recent additions to entertain the tourists.  Plaques like these: Observatory, HM Dockyard Halifax Nova Scotia http://www.halifaxexplosion.net/observatory2.html; Fort Charles, Port-Royal, Jamaica  https://adventuresfromelle.wordpress.com/2018/04/14/port-royal/#jp-carousel-8726 are more promising.  They tie in with the description in the original post, but the phrase ‘harbour marker’ is nowhere to be seen.

Going back to the original post, tiititudorancea.com is actually a tourist web site, so perhaps the whole thing was being used to describe a place they were being advised to visit.  In which case, the original wording might well be more touristy than nautical.  DaveP