1. The 2/84N rule is described in the instructions as a "Universal Slide Rule".
2. After staring at pictures of the rule for a while, one thing which is immediately obvious (yes, I know, the language is not consistent) is the absence of the familiar A, B, C and D scales. In fact the "y" scales perform a similar function to the C and D scales but rather then covering one decade from 1 to 10 they go from 0.65 to 1.5. The Öx plays the role of the A and B scales but covers the range .0045 to 2.3. There are similar peculiarities with the log scales.
3. Whilst the manual (for URL see below) goes into a lot of the mathematics behind slide rules I am not convinced that it really represented an advance in slide rule design. In effect it is a fairly standard log-log slide rule with hyperbolic functions, the only difference being the range of the scales. (But I could be wrong - the manual is not easy to read.)
4. Although listed under 10" rules this rule actually has 8" scales.
5. I also show the earlier 2/84.Some of the differences are:

• The earlier rule is a simplex with two windows in the back whereas as the later one is a true duplex.
• The space of the back of the 2/84 is used for of the tables which appear in the documentation.
• The earlier rule has a much larger cursor but it seems only to have the usual hair lines whereas the later one had marks for decimal point tracking.
• The scales on the front of the rule are the same in both cases.
• The x and y scales only appear on the later rule but the hyperbolic scales are the same.

Please note that some of these images are among the largest on my site but I believe the detail justifies them.

My thanks to John Mosand for the providing scans of the 2/84N and to Jim Bready for the scans of the 2/84.

Thanks to C Redding who upload the file.