4.4 Years 1920-1929

Number of slide rules: 28.

The standard Reitz scale arrangement began to include a CI scale with the K and L, and these scales became more prevalent among many manufacturers. Also, scales for the efficient computation of hyperbolic functions of complex variables (vector scales) were invented at the end of the decade.

Some notable technical developments: first AM radio station, controlled nuclear experiments, development of quantum theory began, TV invented.

Year Maker Model
c.1920 K&E 4088-5
c.1920 Nestler 1a
1921 Faber-Castell 363
1921 K&E 4054
1922 K&E 4035
1922 K&E 4088-3
1922 K&E 4092-3
1922-24 Nestler 37
1923 Faber-Castell 379
1923 K&E 4088-3
1923 K&E 4088-1
1923 K&E 4092-5
1923 K&E 4092-3
1923 K&E 4092-3
1923 Taverniet-Gravet Mannheim
1924 KHH Mannheim Multiphase Adjustable
1925 K&E N4053-3
1925 K&E 4092-3
c.1925 Nestler 41 Pocket
c.1925-1930 KHH Mannheim Multiphase Adjustable
1925-1936 K&E 4058
1928 K&E N4053-3F
c.1928 P.A.S. Co.  Engraving Rule
1928-1933 Nestler 33 Chemiker
1929 K&E Mystery2
1929 K&E 4092-3
1929 K&E 4092-3
1929-1937 K&E 4058C