tag:blogger.com,1999:blog-714718709601620866.post8822997132997611077..comments2024-03-28T04:33:15.006-07:00Comments on David Burch Navigation Blog: Davis Mark 3 Sextant Part 1 — How to read the Angle ScalesDavid Burchhttp://www.blogger.com/profile/13413234790483329339noreply@blogger.comBlogger10125tag:blogger.com,1999:blog-714718709601620866.post-13749803209820245022021-09-23T08:08:24.656-07:002021-09-23T08:08:24.656-07:00Thanks very much Robert. You are right of course a...Thanks very much Robert. You are right of course about that error. The errata is at the bottom of page <a href="https://www.starpath.com/gpsbackup" rel="nofollow">support page</a>, which includes several resources that might be of interest if you have not seem them. This is a little book, but it still took us a while to get what i hope are most of the typos removed. It is now in the 7th printing.David Burchhttps://www.blogger.com/profile/13413234790483329339noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-46206332742970275392021-09-23T03:58:54.004-07:002021-09-23T03:58:54.004-07:00Hi David, I was also looking for the errata, but t...Hi David, I was also looking for the errata, but the page your pointed us to doesn't contain the errors in the calculations I've also found in page 17. In the table 5-2, Lat, as z + Dec, should be 35° 80,6', not 36° 80,6' (thus 36° 20,6', not 37° 20,6'). The error comes from the final Ho, which should be 75° 14,0', not 74° 14,0'.Robert Garrigóshttps://www.blogger.com/profile/08348830734765148288noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-77745658313041910652021-07-31T10:19:22.358-07:002021-07-31T10:19:22.358-07:00Hi Jim, thanks for your comments. There is an erra...Hi Jim, thanks for your comments. There is an <a href="https://www.starpath.com/gpsbackup" rel="nofollow">errata for the latest printing</a> with news about the book. You can send your observations to helpdesk@starpath.com and we will have a look. Thanks.<br /><br />The examples in the book are all presented in a form of sorts, but a separate blank form for the various operations covered seems a good idea. We will look into that and then post it at the page above. I don’t think any of our other forms would be that much help, since the backup methods are so compacted.<br /><br />As for finding Lon from sunrise or sunset, the backup almanac would do the job, but the analysis is not covered in the book, because that calls for learning a full sight reduction which we do not do in this backup approach. When doing that technique, upper or lower or even better both can be used. You can also use sunrise/sunset tables that might be found in tide tables. That approach is covered in our book on <a href="https://www.starpath.com/catalog/books/1830.htm" rel="nofollow"><i>Emergency Navigation</i></a>David Burchhttps://www.blogger.com/profile/13413234790483329339noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-21503824565515289002021-07-31T04:51:16.683-07:002021-07-31T04:51:16.683-07:00I think that I have found a couple on typos in the...I think that I have found a couple on typos in the sample calculations in the book.If these are errors, has an addendum been issued? I will be glad to send you my list, if still needed.<br /><br />I expected a work form for the sight reduction calculations, but was disappointed not to find one. It would serve as a checklist and guide through the process. Has a suitable form just for this been developed? Ideally, the form would be the same size as the book to fit with it in the case.Would one of the standard Starpath Forms serve? Which one would you recommend?<br /><br />There is an excellent article in the blog about determining Long from sunset of the upper limb which only requires a watch, almanac, and probably very dark glasses. Could the book almanac be used? Why not time both the upper and lower limbs?<br /><br />Thanks,<br />Jim LongAnonymoushttps://www.blogger.com/profile/09502889494381083695noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-45977174472775417922020-03-29T20:21:29.281-07:002020-03-29T20:21:29.281-07:00Thanks for your note. The book shown has very deta...Thanks for your note. The book shown has very detailed notes on use of the instrument beyond those covered here.David Burchhttps://www.blogger.com/profile/13413234790483329339noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-40564963943886689852020-03-29T19:14:11.534-07:002020-03-29T19:14:11.534-07:00Thanks for the above explanation of how to read th...Thanks for the above explanation of how to read the vernier calibration I now understand it's application. I have the Davis manual but the instructions are vauge to me and difficult to grasp the concept. The examples you have given are a great.<br /> aid. <br />Yes I get it now. Anonymoushttps://www.blogger.com/profile/07217016540139504665noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-1454130395472216672019-08-21T12:22:52.917-07:002019-08-21T12:22:52.917-07:00To Aaron, on other sextants, the horizon shades a...To Aaron, on other sextants, the horizon shades are primarily for removing glare from the water. If there is no glare on the water, these should not be needed. But on the Mk 3 these second shades are right in front of the eye piece so all light goes through them, meaning they can be used as extra shading in general. The general procedure would be use both of the index shades and then add one or two of the "horizon" shades as needed. If all 4 do not block the sun enough, then maybe they are deficient, or you may have to wait till the sun is lower and less bright. You could also jury rig a homemade solar index shade which would replace the two index shades. That is discussed at the end of this article: http://davidburchnavigation.blogspot.com/2018/09/solar-index-correction-method-for.html and also in our book How to use pastic sextants.David Burchhttps://www.blogger.com/profile/13413234790483329339noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-1084743836335776742019-08-21T12:06:37.985-07:002019-08-21T12:06:37.985-07:00To Axelle, I apologize for missing your question. ...To Axelle, I apologize for missing your question. I think we finally have this set up so we get a notice. By vertical error, i think you refer to what we have called side error. some side error is not crucial, but if too much it won't work. We have notes on adjustments in the book cited and also in another book called How to Use Plastic Sextants. Step one is check for perpendicularity. Then it will be an interactive process using both side error and index error. It is unlikely, but not impossible that the mirror is glued in crooked.David Burchhttps://www.blogger.com/profile/13413234790483329339noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-60608193417480016942019-08-21T11:11:21.899-07:002019-08-21T11:11:21.899-07:00Hi,
I bought a Mark 3 to learn on. For sun sights...Hi,<br /><br />I bought a Mark 3 to learn on. For sun sights, the index shades seem to work well. I see a nice outline of the sun that doesn't hurt to look at. But the horizon shades don't seem strong enough or something. I can't see the outline of the sun because it's lost in all the bright light. (I used both horizon shades). I have stopped using it because I'm worried it might not be good for my eyes. <br /><br />Has anyone else experienced this? Any advice on how to use it correctly?<br /><br />Thanks!<br />Aaronhttps://www.blogger.com/profile/15036970638958274579noreply@blogger.comtag:blogger.com,1999:blog-714718709601620866.post-70014455053654727122019-05-20T09:31:23.138-07:002019-05-20T09:31:23.138-07:00Hello,
We just bought a Mark 3 sextant but for so...Hello,<br /><br />We just bought a Mark 3 sextant but for some reason we can't make the vertical adjustment work: even when the screw is completely loose, a vertical line appears twice (1 on the mirror, 1 in the real world).<br /><br />How important is this adjustment ? Do you know how we could fix this ?<br /><br />Thank you !Axellehttps://www.blogger.com/profile/11422324369911183154noreply@blogger.com