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First post on Forum.

Since early Spring, I have been regularly doing Sun obs's. from my yard. I'm UK based and my home is in the middle of Town, pretty much surrounded by homes and walls, so my sight paths are quite curtailed.

Am using a home-brewed AH, consisting of a square base-board, a shallow black plastic water tray, all covered with a 90-45-45 degrees plate glass pyramid,in section, cover.

I have a bit of an issue in that some unidentifiable force is causing a swirling in the reflective water and, giving an uncertainty of the instant of contact...it cannot be wind, for the glass cover is tight and soon begins to act like a Solar Still.  I have tried Olive oil as a reflector and the swirling is even worse. There has been a noricable and progressive inaccuracy in my results, since early Spring and is presently manifest in "Towards" intercepts of 0.9 arc mins in all  position lines and Transit. I have stable sextant error of nil Side or Perp, just 0.67 arcmin ON the Arc, the same since 1967...taking the micrometer both forward and backward.  Early Spring Intercepts were embarrasingly small. so I have to wonder what is the change.

Sextant has been World Wide with me, a really solid Cooke "Kingston" bought new in 1967, I know it well.

Having thrashed about , for some time, with what is known nowadays as being  a school kids "scientific" calculator, (really?) I  am just one step up from working longhand with Burtons Tables, so I believe my current calcs are free from tables error.

I am wondering, if my environment of massed buildings, is  creating a sort of unquantifiable change in the amount of ordinarily expected Refraction..

Helpfull comments much appreciated.

Loz Elms