# NavList:

## A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding

**Re: SNO-T tests**

**From:**Fred Hebard

**Date:**2005 Nov 28, 12:21 -0500

Alex, Your data look very good. I am not sure, however, that you can attribute the divergence of observation from prediction to arc error with so few data. For instance, the bump at 16 degrees wasn't reproducible between November 13 and November 7. However the Altair- Deneb errors were reproducible (and you got good results with Bill's Astra for the 16 degree measurements). Fred On Nov 21, 2005, at 1:30 PM, Alexandre E Eremenko wrote: > Dear list members, > I want to share some test results of my SNO-T. > (It was bought in Fall 2004 "new", but made in 1990, > has a factory certificate showing correction +10" > everywhere on the arc, which is nonsense, of course. > In summer 2005 I had it checked and certified by BOTH > Freiberger and Cassens-Plath. Freiberger issued a > certificate which shows the following corrections: > > 10d 20d 30d 40d 50d 60d 70d 80d 90d 100d 110d 120d > -4" -4" 10" 6" -1" 4" 5" -5" 4" 4" 3" 14" > > Cassens-Plath wrote only their usual > "This instrument is free of errors for practical use". > > However my multiple careful observations (most of them under > perfect conditions, from a balcony) indicate that there is > some arc error as well as a visible backlash. > (Of course this can always be attributed to insufficient proficiency > of the observer, but consistency of the results I obtain seem to > indicate that my proficiancy is not that bad). > > In all examples below the inverting 7 x 40 scope was used, > I find it by far superior to the 3.5 x 50 Galileo scope. > Sigma stands for mean quadratic error in a series, > SD for the visible radius of the Sun. > To avoid unconscious bias in selection > I include ALL results of the last week of which I have > accurate records. > > IC from Sun, Nov. 17, average of 5 each: > clockwise: -0.42' (4SD=64.72) anticlockwise -0.16' (4SD=64.78) > sigma=0.16' in each case, true 4SD=64.8 > > IC from Sun, Nov. 19, average of 5 each: > clockwise or anticlockwise the same -0.4' (4SD=64.86', true 4SD=64.8') > sigma=0.15', true 4SD=64.8 > > IC from Sun, Nov. 20, average of 5 each: > clockwise: -0.5', anticlockwise -0.4' (4SD=65' in each case, true > 4SD=64.8') > sigma=0.1' > > Index from a star (Rasalhague) Nov. 20. > clockwise: -0.6', anticlockwise -0.2'. > > (This is typical for my index observations from stars. > Sometimes I get -0.7 clockwise and -0.1 anticlockwise, > but the average was always > -0.4 or -0.5 during the last two weeks. In most cases I apply > the average IC=-0.4 or so.) > > Deneb-Rasalhague distance, Nov. 20, 00:40 GMT > Average of 4 clockwise 51d12.0' (sigma=0.0') corrected for index: > 51d11.4' > Average of 4 anticlockwise 51d11.6' (sigma=.2') corrected for > index: 51d11.4' > True distance: 51d11.4' > > Deneb-Rasalhague again, Nov 20, 01:00 GMT > Average of either 4 clockwise or 4 anticlockwise: 51d11.0' > Applying the average IC=-0.4' gives 51d10.6' > True distance: 51d10.7' > > Deneb-Altair distance, Nov 20, 01:30 GMT > Average of 4 clockwise: 38d00.9' (sigma=0) > Average of 5 anticlockwise: 38d00.4' (sigma=0.2) > Total average of all 38d00.6'. Corrected for IC=-0.4 gives 38d00.2' > True distance: 37d59.8' > So we have 0.4' overshot. > > Deneb-Altair distance, Nov 17, 01:25 GMT > Average of 6 clockwise: 38d00.8 (sigma=0) > Average of 6 anticlockwise 38d00.3 (sigma=0.3) > Total average 38d00.6' Correction for IC=-.044 gives 38d00.2' > True distance 37d59.8' > So we have overshot 0.4' > > What can this be is not an arc error? > > Deneb-Vega distance, Nov 20, 02:40 GMT > Average of 4 clockwise: 23d50.1 (sigma=0) > Average of 4 anticlockwise: 23d49.9 (sigma=0.1) > Total average: 23d50.0' correction for IC=-0.4 gives 23d49.6' > True distance 23d49.5' > > Deneb-Vega dist., Nov 13, 23:40 GMT > Average of 4 clockwise: 23d51.3, with IC=-.8 gives 23d50.5' > Average of 4 anti-c: 23d51.0, with IC=-.4 gives 23d50.6' > True distance: 23d50.4' > > Sun-Moon distance of 126 degrees, Nov. 20, 14:40 GMT corrected for > IC=-0.44 > Errors according to Frank's calculator: 0.3', -0.1, 0, 0.1, 0.1. > > Sun-Moon distance of 137 degrees (maximum SNO arc allows! one can go > a bit further, to 141 degrees by detaching the magnifying glass:-) > > Nov. 19, 14:40 GMT, corrected for IC=-0.4 > Errors according to Frank's calculator: -0.2', 0.1', 0.3'. > (One blunder discarded, error 0.7') > > Mars-Moon distance of 40 degrees > Nov. 18, 3:30 GMT, corrected for IC=-0.4' > Errors according to Frank's calculator: -0.3', 0.8', 0.2', 0.7', 0.7', > 0.6' then checked the Frank calculator, and repeated the series, > trying > to see whether I can match somehow the numbers calculator gives:-) > -0.1', 0.5', -0.1', -0.2', -0.5', > 0.3', 0.1', -0.1':-) > > Mars-Moon distance at 16 degrees > Nov 13, 1:30 GMT, IC=-0.4' > Errors: 1.0', 0.6', 0.8', 0.2', 0.7' > > Same, with Bill's Astra, same evening, with the SAME inverting scope: > Mars-Moon at 16 degrees, Nov 13, 1:30 GMT IC=+0.35 > Errors: -0.1', 0.1', -0.1', 0.2', -0.1' > > Can I conclude that my arc has a huge bump at 16 degrees? > > However: > Venus-Moon November 7, GMT 0:30 at 15 degrees, IC=-0.4 > Errors: -0.1', 0', 0'. > > Mars-Moon distance Nov. 18 at GMT 3:20, at 40 degrees, IC=-0.4 (SNO > again) > Errors: -0.1', 0.5', -0.1', -0.2', -0.5', 0.3', 0.1', -0.1'. > > Sun, art horizon, oil over syrup, Nov. 20, 19:20 GMT IC=-0.4, watch > exact. > Antickockwise, UL: > > 19:28:20 48d42.8' > 19:29:50 48d25.3' > 19:31:00 48d10.9' > 19:32:32 47d52.9' > 19:33.54 47d36.7' > > Averages: 19:31:07 48d09.7' > Error: -0.2 (undershot). But actually this means -0.4 because > the measured altitude was divided by 2. > > Any comments? > (I can supply more details on each observation if anyone is interested > I would be very interested to see analogous data posted (or sent to > me) > by other people practicing without real horizon). > > Disclaimer for George: > I understand that the issues discussed here are far from the > practical needs of a small-boat navigator:-) Still I think these are > proper questions for discussion on this list. My concern is whether > I can take reliable Lunars under good conditions from land to 0.2' > precision, > and whether it is possible at all, and whether it is possible with > my SNO-T. > > Alex.