1. If only the function of all rules was clear from the name as this one is.
2. The one factor whih differentiates this rule from others is presence of trig scales on both the slide and the stock. The sin scales being used with the A and B scales and the tan scales with the C and D scales.
3. The tables and factors on the back of the rule were also geared very much to navigation. Two samples are shown below.
4. One rather unusual table is the one on the bottom right -  a guide for estimating wind speed.
5. Also unusual are the measurement scales on the edges of the rules; one at 1:1 000 000 and the other at 1: 500 000
6. It is also clear that this slide rule had been kept in box when not in use. Unique rules have paper scales covered with clear plastic and the paper had a tendency to go yellow - this rule's scales are almost pure white!
7. I bought this rule at the same time as the Faber Castell 67/38 Tachymeter, which also have a larger than usual range of trig scales so they were probably owned by the same person.
8. The price of the rule, stamped on the box was, 13/6, (£0.675  or about $1).