I have since learnt that its best to HAVE AN ASSISTANT, lower the line FIRST and keep up from the slab about 1.5 metres,THEN rest the bob on your knee, and screw the nut into the bob, allow for 500 mm of take up, and slowly lower.
DON'T do as a one man operation like I did in another asian country, dont lower the bob over the edge, hence the line gets cut buy a sharp edge in the threaded nut, and you watch the bob fall from halfway down,and drops about 30 metres, in a cordened off area, but 5 metres from a little guy sweeping the floor.
No, they dont bounce, and suprisingly the tip never dulled, but i did have to go down and file and incident report, bloody stupid of me, for that, and using nylon line.
I have found that piano is wire prone to snapping, kinking from constant use, whereas the multistrand trace wire is heaps better to roll up on a reel,stronger, safer and easier for the bob to stay central on the axis.
I do prefer piano wire for one off checks outside, because the wire is thinner in the wind, having done calcs, the bob doesnt move, whereas the thicker multi-strand does get affected at times due to its greater area, but not as great inconvienience.
Plumbobs of this size are not used much, but they have helped me many times in hard to get at places and to settle arguments between various surveyors, and the methods they used in the first place to layout a point.
Its like the surveyor on my last job who checked stair risers and gave concrete levels with a total station, too much faith in the specs, but coulndnt see the light.
My email about the plummet is [email protected]. sorry about the double post and thanks to those who replied.
Cheers
David