6.7 Numerous Scales
Here we present the slide rules that have the largest number of distinct scales, presently those with 24 scales or more. We designate as a single “scale” a single line or path that extends across the length or circumference of the rule without interruption. Certain scales, for example the Log-Log scales, are often broken up into a series of scales; so, one could argue that a 25 cm slide rule that breaks a Log-Log scale into four parts (LL0, LL1, LL2, and LL3, say) has a 100 cm Log-Log scale. For this list, however, we are treating these as four separate scales. On the other hand, a spiral Log-Log scale that wraps around a circular slide rule 5 times would be designated as a single scale. Measurement scales (inches, centimeters, etc., mostly found on the older rules) are not counted in the sum.
The mean number of scales on the rules of the collection is 13.3, with a median number of scales equal to 11. Below is a histogram of the number of scales found on the slide rules of the collection. Note the bi-modal nature of the distribution, which shows a large peak at about 8 scales, and another distinct distribution centered at about 22 scales. One might argue that the distinction between a “basic” slide rule and an “advanced” slide rule is showing up. (See Why Slide Rules?.)
The time progression of the distribution can be seen below.
|Blundell Rules Limited||506 Academy Duplex||1970-1980||L||10||24|
|Boykin||RotaRule Model 510||1965||S||50||24|