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Brett. My plot used to be a slate quarry, I dont know if slate is reactive?. Being right next to a cliff, mmm, solid slate, I dont see it cracking, but yes that might be a point. The next pier will be deeper, thats for sure.
Rally. Its on top of a cliff, next to a huge excavated hole (the whole street), that was a quarry, but some 35yrs ago, perhaps the ground hasnt settled yet from that activity. Its just dawned on me that the OBs is also right next to a really massive tree, I suppose its growth would constantly shift the ground.
I havent kept track of the drift to see if it goes back and forth with the seasons, good point, ill log that. Being on a cliff, the drainage is excellent.
The beer factor causing inadvertent mount-bumping might be a factor too.
Guy. Yes, AO gets bad very quickly with polar alignment drift, causing too many mount bumps, its the first indication of drift. Seasonal checks is the go, as you say.
Steve. A laser to have a quick indication of drift is a nifty idea. I use Tpoint to precisely measure alignment though, not drift, as it is quicker and also shows a report of exactly how many knob ticks to adjust the mount. Its usually done with 2 attempts within arc/secs.
James. Its 20 arc/mins in one axis only (cant remember which one) the other was 5 odd over the whole 4 mths. I have adjusted it a few times during that time, the last time being the worst, some 4 tics. Come to think of it, it has rained more over the last 2 mths than usual.
Dr Paul. A large slab, mmm, its not often you hear of that, wouldnt the slab have to be very large?. Then you would have to float a larger floor over it, to keep it isolated from walking in the OBs?
Barry. Well there you go, a slab. 2.4m square?, thats just 1.2 * 1.2m, I think that would be too small for a PME, but anyway it works for you so I guess a slab must be possible generally, so why isnt it more common?. Im looking for single digit arc/sec alignment too.
Greg. Thats interesting, but the Parkes scope would have an insane FL I suppose (mmm, I wonder what it is?). Yes, Tpoint is luckely quick and easy to use.
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