Pickett 101-C Dial Rule

The duplex 101-C circular rule was produced in the United states since 1950 until 1975. Fabricated with aluminum coated with an eye saver yellow thin plastic where scales were photo printed on, it had three clear plastic indicators, two at the front face and one at the back face. All indicators had a hairline and two of them, one at front and the one at back, have engraved the scales labels.

With 17 scales, this rule was very useful for Students, professionals, and specially machinists and mechanical engineers. The scales on the 101-C are: C, CI, A, A^F, L, F^A, LL², LL¹, DS, DT, M on the front face, and C, S, ST, T, Fractions-Decimals on the back face. One interesting and not very common characteristic of the 101-C is the presence of two A-scales: A, A^F, the first one subdivided decimally, and the second one divided by the common fraction system (1/2's, 1/4's, 1/8's, 1/16's, and 1/64's), to quickly find the square root of fractional numbers. Another fractional scale on the 101-C is F^A , this gives the fraction corresponding to the numbers on scale L.

Other special scales are DS-DT, designed to find drill sizes and double depth of threads. Using DS with L (or F^A) is possible to find the size of a drill specified by the letter or number read on DS. The DT scale, used with the L-scale, gives the number of threads per inch (See User Manual).

The last special scale on the 101-C is M. Used with the L-scale is possible to convert directly inches-millimetres. I have not seen other Pickett rules with the same set of special scales. Only the circular 103-ES Markup Calculator has the scales A^F and F^A, as well as the fraction-decimal conversion table .

The with the logo on the model in this collection, this was manufactured between 1959-1962:

Click on the next links to see professional panoramic pictures of the 101-C model.

https://www.sliderulemuseum.com/Pickett/Pickett_101-C_Dial-Rule_DonatedByAnnKilby.jpg