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I started off this hobby trying to find my True South line using an expensive Silva compass with magnetic declination at both my Sydney location and South Coast NSW location and found that my polar alignment after the initial or first iteration was way off , up to 4 degrees.Every time I used it there were significantly different readings. I noticed the closer the compass was to the ground the deviations were worse and on the ground were all over the place ( obviously picking up iron sources somewhere.For every set up I was meticulous in setting up the tripod , levelling , orientation, latitude settings and so on , even using right angled set squares etc.... and so on
I thought there’s gotta be a more consistent reliable method to find True South and permanently score a line on the ground for repeated use at both sites.
The penny dropped from my scouting days , Solar Noon Shadow method
So set up a 1.2m high 12mm dia rod ( painted black ) at 90 degrees with guy strings anchored NSEW for fine adjustin. Waited for exact Solar Noon time and marked the centre of the shadow as precise as possible with a thin indelible marker.
Set up my tripod meticulously aligned to the new Solar Noon True South line. Performed my polar alignment routine and after the first iteration ended up only 5 or 6 arc minutes away.Both locations ended up with really accurate initial PA and usually only require another couple of iterations to get below an arc minute
So sold the Silva compass and now I have my extremely accurate permanent True South lines at both sites thanks to the good old Sun.
Nothing wrong using the compass but I found it had poor reliability ( not always the same line )
NB: Also at both sites the ground is laid pavers not concrete but fairly level ( if your out in the bush with uneven ground you would need a flat bit of plywood to use to mark your line.
My experience.........
Cheers
Martin
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