Faber & Castell
2/83N
Novo Duplex

 Known as the Best Slide Rule.
 W1W2 and W1'W2' scales (square Roots, same as R1R2) show an effect of double length (50cm, 20inch).
 Include good scales:
P (Pythagorean, sqrt(1X²) ) scale,
red complementary angles and T1T2 (extended tangent) scales.

A half size of this, pocket model 62/83N, is the most attractive slide rule.
