# NavList:

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

Message:αβγ
Message:abc
 Add Images & Files Posting Code: Name: Email:
From: Gary LaPook
Date: 2016 Nov 12, 01:28 +0000
I checked you computation of the current correction angle in section 28 of your manual. Your numbers:

boat speed   =   6.5 k
current angle relative to the course  =   30 degrees
current correction angle     = 10.2 degrees
SOG (current from ahead)    =   4.45 k
SOG (from the stern)    =            8.35 k

Doing the same calculation on a calculator I get:

boat speed   =   6.5 k
current angle relative to the course  =   30 degrees
current correction angle     = 10.19058877 degrees
SOG (current from ahead)    =   4.405602005 k
SOG (from the stern)    =            8.389318862 k

This computation is done by use of the law of sines.

I'm making a point. Since your input speeds are only to a one-tenth of a knot precision and the course to one degree, it makes no sense to state the results to one-hundredths of a knot and the current correction angle to one-tenth of a degree (can you steer that well with your compass?) Note that your SOGs are wrong, they should be, rounded to one-hundredths of a knot, as 4.41 k (yours is off by 0.04 k) and 8.39 (yours is also off by 0.04 K.)

gl

To: garylapook@pacbell.net
Sent: Thursday, November 10, 2016 1:33 PM

I am attaching a revised user manual and drawings for the Mark 2 Navigator's Slide Rule.
Changes to the Manual:
• A number of errors have been eliminated, including a serious error on what is now page 51.
• Sections 4 and 26 on Speed, Time and Distance have been significantly revised.
• Sections 5 and 31 have been added, on using a Dutch log.
• Sections 6 and 28 have been added, on solving a current triangle.
• Sections 18 and 43 have been added, on solving a rhumb line course.
• One additional bibliographic citation (Martenhoff).
Changes to the rule itself:
• It retains the recently added Ln scale, for use in rhumb line calculations.
• A gauge point has been added at 314... (π) for use in rhumb line calculations.
• A gauge point has been added at 592... for use with a Dutch log.
I have been grateful for the feedback I have received, and will continue to be grateful for further suggestions and help.  My goal is to have the design finalized prior to the end of this year, and then proceed to fabrication.
Bob

Attached File:
_Mark-2-Slide-Rule-Back-Side.pdf

Attached File:
_Mark-2-Slide-Rule-Front-Side.pdf

Attached File:
_Mark-2-Slide-Rule-User-Manual.pdf

Browse Files

Drop Files

### Join NavList

 Name: (please, no nicknames or handles) Email:
 Do you want to receive all group messages by email? Yes No
You can also join by posting. Your first on-topic post automatically makes you a member.

### Posting Code

Enter the email address associated with your NavList messages. Your posting code will be emailed to you immediately.
 Email:

### Email Settings

 Posting Code:

### Custom Index

 Subject: Author: Start date: (yyyymm dd) End date: (yyyymm dd)