The Decimal Point and Slide Rule Answers

The placing of the decimal point in the slide rule answer is frequently done through a process of estimating the approximate answer and making placement accordingly.1 For some people, the method Is sometimes time-consuming as well as productive of incorrect conclusions. Shuster2 found that slide rule learners experience considerable difficulty in using this method—indeed, 33.4% of the errors made by the students in his study came from this source. Shuster recommended the “standard number” system3 as being a more desirable method of meeting the problem of the straying decimal point. A method, arising out of the logarithmic nature of the slide rule, is presented here. This method is explained only in connection with its application to the C- and D-scales. It may, however, be extended to include all scales on the Log Log Duplex Trig slide rule.4