I have always used Sokkia B series levels, but am interested in buying a Zeiss Ni30 or Ni40 off ebay. They seem to have stopped making them about a decade ago, but their appeal for me is a) Renowned optics, and b) the bubble apparently moves the "right" way when viewed in the mirror! I like the sound of that.
Looking at the following:
http://www.geotrade.hu/index.php?page=letoltes&spage=fajl&id=69
http://www.sokkia.com.sg/products/automatic/uploads/B20_B21.pdf
For an Ni30, a "mean error" for a 1km run of 1mm.
For a Sokkia B21, a standard deviation for a 1km run of 1mm.
Same thing? I didn't think "mean error" was a proper error propogation term, so it seems a bit suprising coming from Zeiss - but if the bubble really does move the right way in the mirror, I'm prepared to forgive them!
http://www.gpprague.cz/en/second_hand_instruments.html
http://www.meraj.sk/SECOND-HAND-POUZITE-PRISTROJE
http://gpprague.cz/eshop/pristroje-nivelacni-pristroje-c-13_19_55_260.html
😉
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Thanks for those links. Good luck with the business. - I guess I buried my actual question - whether mean error is the same as standard deviation - too deeply in all my waffling...