THACHER's  SLIDE RULE
by Keuffel & Esser, NewYork

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 ``` T H A C H E R ' s SLIDE RULE Model » 4012 « ********************************************************************* Keuffel & Esser, NewYork / USA (1917) SN = 4689 S C A L E C O N F I G U R A T I O N OF THE THACHER's SLIDE RULE ===================================================================== The 30' scales are segmented in 18" scales having 2 portions each: An EXTERNAL Segmented Cylinder that rotates with Scales ... UP LOOKING ------------------------------------------- LOOKING UP | LEFT-C = sqrt(X) if X has ODD No. of Digits | | RIGHT-C = sqrt(X) if X has EVEN No. of Digits | | B = X 20 Segments | =============================================================== | A = X 20 Segments | +-------------------------------------------------------------+ O== A movable INTERNAL Cylinder that also rotates w. Scales ... ==O +-------------------------------------------------------------+ | A' = X' ( 9" left-shifted X ) 20 Segments | =============================================================== | B' = X' ( 9" left-shifted X ) 20 Segments | | RIGHT-C' = sqrt(X') if X' has EVEN No. of Digits | | LEFT-C' = sqrt(X') if X' has ODD No. of Digits | DOWN LOOKING --------------------------------------- LOOKING DOWN E X A M P L E S ( from the Instruction Book, p.16 ) **************************************************** PROPORTIONS: A / B = A' / B' <==> A / A' = B / B' MULTIPLICATION: [ B = 1 ] ===> A' = A * B' DIVISION: [ A' = 1 ] ===> A = B / B' MULTIPLICATION (Fig.4) 5 x 106 = 530 DIVISION (Fig.5) 282 / 3 = 94 E X A M P L E TO DEMONSTRATE THE PRECISION OF THE » THACHER « SR ===================================================================== D I V I S I O N 355 / 113 = 3.141592920 in alternative ways ... ===================================================================== ( R E M A R K : π = 3.141592654... APPROXIMATION ) B 355 B ---------------------+------------------ A 113 A ... ... B 3.1416 B ----------------+----------------------- A 1 A or A' 113 A' ------+--------------------------------- B' 355 B' ... A' 1 A' ---------------------------------+------ B' 3.1416 B' ====== Back to the THACHER's Main Page ... impressum: ********************************************************************* © C.HAMANN http://public.beuth-hochschule.de/~hamann 01/22/14 ```