NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: micrometer sextants.
From: Brad Morris
Date: 2009 Jul 17, 15:36 -0400
From: Brad Morris
Date: 2009 Jul 17, 15:36 -0400
Hi Wolfgang Yes, the classic discussion of resolution, accuracy and repeatability. Resolution is where your tick marks are. You can have as many as you want. Resolution, however, is not accuracy. Consider, I can have many tick marks, but there is no statement as to the accuracy of those tick marks. In other words, you can have very fine resolution without any accuracy whatsoever. Now accuracy is the relationship of the index arm to the graduated arc. When the index arm points to a number, is it correct? Finally, the repeatability of the measurement can be considered. Are you only using the micrometer in one direction (uni-directional repeatability) or both (bi-directional repeatability). If bi-directional repeatability is considered, will you examine lost motion (gear play, thrust springs, etc). Even uni-directional repeatability will have errors due to the slip stick behaviour of mechanisms. ------ Just because a sextant has a micrometer drum, doesn't make it any better than the older style vernier, in terms of resolution, accuracy or repeatability. It is "easier to read" if a person can't be bothered to learn how to read a vernier. It looks "high tech" and as such will appeal to the target market. The vernier is superior because there is no gear train and hence no lost motion. Best Regards Brad "Confidentiality and Privilege Notice The information transmitted by this electronic mail (and any attachments) is being sent by or on behalf of Tactronics; it is intended for the exclusive use of the addressee named above and may constitute information that is privileged or confidential or otherwise legally exempt from disclosure. If you are not the addressee or an employee or agent responsible for delivering this message to same, you are not authorized to retain, read, copy or disseminate this electronic mail (or any attachments) or any part thereof. If you have received this electronic mail (and any attachments) in error, please call us immediately and send written confirmation that same has been deleted from your system. Thank you." --~--~---------~--~----~------------~-------~--~----~ NavList message boards: www.fer3.com/arc Or post by email to: NavList@fer3.com To , email NavList-@fer3.com -~----------~----~----~----~------~----~------~--~---