Promotional slide rule, Concrete Volume, plastic / cardboard, made by Blundell Harling Ltd, England, 1970-1980
This slide rule is from the collection of calculating instruments assembled by Assoc. Professor Allan Bromley. His collection provides examples of most forms of calculating devices made from the early 18th to the late 20th centuries. Slide rules constitute a substantial proportion of this collection.
Over the 19th and much of the 20th centuries the slide rule was the primary instrument for calculation used by many people engaged in the trades and in engineering. Although originally invented in the 17th century, and widely used for gauging (or estimating the quantities of certain products such as alcoholic spirits) it took until around 1850 for the slide rule to become generally popular. However for those engaged in estimating (ie, gauging) various quantities of goods in use in the liquor, building and agriculture trades, and for calculating the excise duty to be paid on these goods, numerous kinds of sliding rules with useful scales were developed.
Specialist slide rules of many kinds were developed over the period of their use. In the 20th century many special purpose slide rules were made from various kinds of paper or card, and from light sheet plastics once plastics became a common place in the later part of the century. Generally known as Perrygrafs after the Perry Graf Corp of Maywood Illinois, [Johns] who made slide charts and rules and other speciality items for marketing purposes, they were commonly made as promotional devices while retaining some functional value.
This slide rule was designed to assist in the calculation of the volume of cement to be used in concretes of particular mix proportions. It uses Imperial units on one side and Metric units on the other and must have been made about the time of the changeover from Imperial units to Metric units in Australia. Given the length and width of an area and the depth of the concrete slab, the volume of concrete in cubic yards or cubic metres can be calculated. It was made for Australian Blue Metal (Darwin) as a promotional item.
Made for Australian Blue Metal (Darwin), A Division of Readymix Group, S.A.
Supplied by Australian Data Converters (Adelaide). Mfr'd by Blundell Harling Ltd, Weymouth, England.
Australian Blue Metal was established by the O'Neill family of Perth to quarry basalt in the early 1950s. They were taken over by Readymix in 1957 who were subsequently engaged in the sealing of the highway across the Nullarbor. Readymix later became a subsidiary of CSR Ltd.