 Jan 2024

www.mccoyskecatalogs.com www.mccoyskecatalogs.com

1956  The ST scale on rules that had Decimal Trig scales were converted to an SRT scale.

1956 0 88,500 88,500
My 41813 slide rule was likely manufactured in 1956 as it has the SRT scale initiated in 1955 and has a serial number 004365 which is in the series 3 segment which reset in 1956 and ran from 0 to 88,500 that year.
https://www.mccoyskecatalogs.com/keserialnumbers/Dating2.htm


www.mccoyskecatalogs.com www.mccoyskecatalogs.com

www.mccoyskecatalogs.com www.mccoyskecatalogs.com

www.mccoyskecatalogs.com www.mccoyskecatalogs.com

1955b  The scale set was changed. ST scale was changed to SRT on the 4081s only.
My 41813 was likely made in 1955 or after as it has the SRT and not the ST scale. (It has a 1947 copyright mark on it.)

1955b (40813, 40815, 41811, 41811C, E4181J, 41813, 68 1200, 68 1205, 68 1210, 68 1215, 68 1220, 68 1251, 68 1256, 68 1261, 68 1282, & 68 1287) Scale sets: Front: LL02 LL03 DF = CF CIF CI C = D LL3 LL2 Rear: LL01 L K A = B T SRT S = D DI LL1
These are the scale sets on my K+E 41813 slide Rule


www.mccoyskecatalogs.com www.mccoyskecatalogs.com

41813 10" Log Log Duplex Decitrig Plastic 40813 family
The Keuffel & Esser 41813 was part of the 40813 family and was described in their catalogs as a 10 inch Log Log Duplex Decitrig Plastic slide rule.
via https://www.mccoyskecatalogs.com/KEModels/kexrefmain.htm



Either index may be used.
If the numbers to be multiplied result in the hairline not being able to be used because the reading is off one side of the slide rule, then use the second index (the number 1) on the D scale.

To find the product of two numbers, disregard the decimalpoints, opposite either of the numbers on the D scale set the index ofthe C scale, push the hairline of the indicator to the second numberon the C scale, and read the answer under the hairline of the D scale.The decimal point is placed in accordance with the result of a roughcalculation.

Definitions. The central sliding part of the rule is called theslide, the other part the body. The glass runner is called the indicator and the line on the indicator is referred to as the hairline.

Kells, Lyman M., Willis F. Kern, and James R. Bland. K+E Slide Rules: A Self Instruction Manual. New York: Keuffel & Esser Co., 1955.

Accuracy of the slide rule. From thediscussion of § 2 it appears that we read fourfigures of a result on one part of the scaleand three figures on the remaining part.Assuming that the error of a reading is onetenth of the smallest interval following thelefthand index of D, we conclude that theerror is roughly 1 in 1000 or one tenth of oneper cent. The effect of the assumed errorin judging a distance is inversely proportional to the length of the rule. Hencewe associate with a 10inch slide rule anerror of one tenth of one per cent, with a20inch slide rule an error of one twentiethof one per cent or 1 part in 2000, and withthe Thacher Cylindrical slide rule an errorof a hundredth of one per cent or one part.in 10,000. The accuracy obtainable withthe 10inch slide rule is sufficient for manypractical purposes; in any ease the sliderule result serves as a check.
The accuracy of most 10 inch slide rules is approximately 1 in 1000 or one tenth of one percent.
Because the error in approximating distance is inversely proportion to the length of a slide rule, longer slide rules will have proportionally smaller errors, so while a 10 inch slide rule has an error of 1 in 1000, a 20 inch will have an error of 1 in 2000 and larger rules can be accurate to within 1 in 10,000 or better.



KE Keuffel & Esser Slide Rule Model 41813 & Leather Case

 Aug 2023

www.reddit.com www.reddit.com
 Mar 2022

www.sliderulemuseum.com www.sliderulemuseum.com