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no i do it totaly with the marks on the left. for instance if i set the horizontal on the waterline as if you were going to use the stadimeter. but then i line the mast up with the marks on the left then count down from the top. i count each mark as 20, so if its 10 marks then 20 x the mast heigth divided by the the marks up from the horizontal line gives the range
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Yup, that's correct, as it means using the "stadia", where the stadimeter takes its name from
http://en.wikipedia.org/wiki/Stadia_rod#Stadia_rods
http://mysite.du.edu/~jcalvert/astro/stadia.htm
http://www.fao.org/docrep/field/003/E7171E/E7171E03.htm