Very cool, I've never used a slide ruler but I can see how in logarithmic space, that 3.3/2 scaling factor simply becomes a distance you add.

Makes me want to get one now, because I like the concept of memorizing ratios rather than recipes (thanks to the popular eponymous book), and this seems more convenient (and satisfying) for non-trivial computations than getting my screen dirty or dictating it to an assistant.