Known as the Best Slide Rule.

W1-W2 and W1'-W2' scales (square Roots, same as R1-R2) show an effect of double length (50cm, 20inch).

Include good scales:
P (Pythagorean, sqrt(1-X²) ) scale,
red complementary angles and T1-T2 (extended tangent) scales.

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