## 6.6 Non-Linear and Long-Scale Rules

Most people first recognize slide rules as linear devices, though circular logarithmic sliding scales were developed very early in the 1600s, including by Oughtred himself. And, in addition to scales in the shape of circles, slide rules were also created that contain other shaped curves, such as spirals on a circular platform, or even three-dimensional helical scales on the surfaces of cylinders. One major advantage of these “non-linear” designs is to provide a longer logarithmic scale to produce greater accuracy in reading and setting the numbers on the scale; or, consequently, a smaller device can be created with just as much or more accuracy as might be found on a longer “linear” rule with larger dimensions. Below we list all the items in the Collection whose scales are not straight linear scales. Also presented in our second list are those with longer than typical scale lengths for performing standard calculations (i.e., specialty slide rules are generally excluded from this list).

Two different lengths are indicated in the tables below. First, L0 is the length in inches of a single decade of the main scale (e.g., C, D) on the rule. The second parameter, Lx, is the length in inches of the slide rule’s maximum dimension. Note that the value of L0 for a typical linear slide rule is approximately 10 inches (25 cm). The first list below tabulates all slide rules in the collection that are not linear slide rules (i.e., circular, spiral, and helical slide rules). The second list has any standard slide rule with L0 greater than the standard 10 inches (25 cm).

Non-Linear Slide Rules

Maker Model Year Type Mat L0 Lx
Stanley London Fuller’s Calculator Model No. 1 1909 H wd 500.0 12.0
Gilson Atlas
1931 S Al 468.0 8.0
Otis King Model L 1949 H ss 66.0 6.0
Otis King Model K 1965 H ss 66.0 6.0
Felsenthal AN 5837-1 1943 C pl 60.0 8.0
Boykin RotaRule Model 510 1965 S pl 50.0 6.0
Sillcocks-Miller M1 Slide Rule No. 547 1942 C pl 31.0 12.0
Fowler Long-Scale 1943 C ss 30.0 3.0
Palmer Palmer’s Computing Scale 1843 C pp 27.0 11.0
Gilson Binary 1941 C Al 26.0 9.0
Kahl Scientific Culbertson Slide Rule 1955 C pl 24.0 8.0
Felsenthal FAA-95 1950-1955 C pl 16.0 8.0
C-Thru PS-79
1970 C pl 16.0 6.0
C-Thru S-96
1973 C pl 15.0 6.0
Gilson Midget 1919 C Al 12.0 4.0
Gilson Midget
1940 C Al 12.0 4.0
Felsenthal D-4 1944 C pl 12.0 4.0
Felsenthal Logarithmic Calculator FF-6 1951 C pl 12.0 5.0
Concise 270
1955 C pl 12.0 4.0
Pickett 101-C 1962-1964 C Al 12.0 4.0
Fearns Calculators A13
1970 C pl 12.0 5.0
Palmer Palmer’s Pocket Scale 1845 C pp 10.0 3.0
Felsenthal Dial-A-Con 1968 C pl 9.0 7.0
Concise 600ST 1969 C pl 8.0 3.0
Concise 28
1970 C pl 8.0 4.0
Halden Calculex
1918 C ss 6.3 2.5
Graphic Calculator Percentage Calculator 1962 C pl 5.0 6.0
MATSKU KL-1 1969 C ss 5.0 2.0
Blundell Rules Limited Radiac No. 1 1952-1956 C pl 2.0 5.0
Concise 380
1959-1966 C pl 2.0 4.0
USSR Military Slide Rule RL 1970 C pl 2.0 7.0

Long-Scale Slide Rules

Maker Model Year Type Mat L0 Lx
Stanley London Fuller’s Calculator Model No. 1 1909 H wd 500.00 12
Gilson Atlas
1931 S Al 468.00 8
K&E 4013 Thacher 1907 L wd 360.00 18
Otis King Model L 1949 H ss 66.00 6
Otis King Model K 1965 H ss 66.00 6
Boykin RotaRule Model 510 1965 S pl 50.00 6
Pickett N1010-ES Trig Demonstration
1958 L wd 40.00 48
Fowler Long-Scale 1943 C ss 30.00 3
Palmer Palmer’s Computing Scale 1843 C pp 27.00 11
Gilson Binary 1941 C Al 26.00 9
Scofield Engineer’s Slide Rule 1901 L wd 22.00 24
K&E 4088-5
1920 L wd 20.00 20
K&E 4092-5 1923 L wd 20.00 20
Nestler 24
1930 L wd 20.00 20
K&E N4096 1935 L wd 20.00 20
K&E N4092-5 1936 L wd 20.00 20
K&E N4053-5 1937 L wd 20.00 20
K&E 4081-5 1956 L wd 20.00 20
Aristo 1067U 1961 L pl 20.00 20
K&E 4083
1916 L wd 16.00 16
C-Thru S-96
1973 C pl 15.00 6
noID Gunter Rule
1820 L wd 12.00 24
Dring and Fage Inland Revenue Rule 1883-1902 L wd 12.00 24
Gilson Midget 1919 C Al 12.00 4
Gilson Midget
1940 C Al 12.00 4
Felsenthal Logarithmic Calculator FF-6 1951 C pl 12.00 5
Concise 270
1955 C pl 12.00 4
Pickett 101-C 1962-1964 C Al 12.00 4
Fearns Calculators A13
1970 C pl 12.00 5
Davies Routledge Engineer
1840 L wd 11.00 12
Stanley No. 15
1858 L wd 11.00 12
E.S.A. London Harrow Mark Reducer 1898-1925 L wd 11.00 36
Belcher Bros.  Engineer’s Rule 1831-1843 L wd 10.25 12

Note: The following slide rules are special cases in so far as scale length is concerned.

• The Fowler Long Scale Calculator is a segmented-scale rule with major scale made up of 6 individual circular scales totaling 30 inches in length.
• Thacher’s Calculating Instrument is also a segmented-scale rule, made up of 40 individual linear scales totaling 360 inches in length.

Distribution of Primary Scale Lengths for Entire Collection: