Scale rules are tools used to measure distances on scale drawings and physical models, allowing for precise calculations of actual object dimensions based on the drawing’s scale. A scale rule indicates the relationship between a drawing’s dimensions and the actual object’s dimensions, so a scale of 1:50 means that 1 unit on the drawing represents 50 units in real life. By aligning the ruler with a measurement on the drawing, you can directly read the corresponding actual dimension in real-world units.
Verulam
Verulam refers to a brand of scale rules, primarily used in architectural, engineering, and surveying professions. Some Verulam scale rules are RIBA (Royal Institute of British Architects) approved, indicating their compliance with professional standards.
Verulam was originally registered as a Trade Mark in 1961 by Blundell Harling Limited under ‘Measuring apparatus and instruments, slide rules, protractors included in Class 9, and parts included in Class 9 of all the aforesaid goods.‘. The registration expired in September 2016 and it was removed from the register in March 2017.
Further information with thanks to Designer Buildings – Whilst a conventional ruler allows measurement of full scale (1:1) dimensions, a scale rule also allows measurement of drawings that are not at full scale without the need for any conversion. Whilst a conventional ruler allows measurement of full scale (1:1) dimensions, a scale rule also allows measurement of drawings that are not at full scale without the need for any conversion.
Scale rules typically measure full scale dimensions up to 300mm. They are generally either flat (actually a flat oval shape), similar to a conventional ruler, with 8 different scales along their four edges (2 on each edge), or a three-pronged star shape (generally referred to as triangular) with 12 different scales along their 6 edges.
The scales on a four-edged flat scale rule are generally: 1:1, 1:100, 1:20, 1:200, 1:5, 1:50, 1:1250 and 1:2500. The scales on a 6 edged triangular scale rule are generally: 1:1, 1:10, 1:2, 1:20, 1:5, 1:50, 1:100, 1:200, 1:500, 1:1000, 1:1250 and 1:2500. However, they may only have 6 scales, one on each edge: 1:20, 1:25, 1:50, 1:75, 1:100 and 1:125.
In Britain, for flat rules, the paired scales often found on architect’s scales are:
- 1:1/1:10
- 1:5/1:50
- 1:10/1:100
- 1:20/1:200
- 1:1250/1:2500
For triangular rules, the paired scales are:
- 1:1/1:10
- 1:2/1:20
- 1:5/1:50
- 1:100/1:200
- 1:500/1:1000
- 1:1250/1:2500
Less common scales are:
- 1:25/1:250
- 1:331⁄3
- 2:1
A Scale Selector Chart sourced from scalerulers.com is available here
History of Scale Rules
Scale rules have a history rooted in the need for accurate measurement and representation of objects or areas at a reduced size. Early forms included logarithmic scales, like Gunter’s scale, used for navigation and calculations. Later, slide rules emerged, combining two logarithmic scales for direct calculations, and then evolved into various forms, including circular and linear designs. Engineering and drafting scales further developed to represent objects at specific ratios, aiding in blueprints and other technical drawings.
Early Development:
- Need for Measurement: The fundamental need for measuring lengths and distances has been a driving force in the development of scales.
- Body Parts as Measures: In early times, people used body parts like hands and feet as reference points for measurement.
- Early Measuring Instruments: The earliest known uniform systems of weights and measures were created in ancient civilizations like Egypt, Mesopotamia, and the Indus Valley.
The Rise of Logarithmic Scales:
- Napier’s Logarithms: John Napier‘s invention of logarithms in 1614 paved the way for more efficient calculation methods.
- Gunter’s Scale: Edmund Gunter, an English clergyman, developed a scale where logarithms could be used for multiplication and division, known as Gunter’s scale.
- Dividers for Calculation: Gunter’s scale used a pair of dividers to measure the distance between logarithmic numbers, enabling multiplication and division.
Slide Rules Emerge:
- Oughtred’s Contribution: William Oughtred, in the 1620s, combined two Gunter scales and slid them together, allowing for direct calculations without dividers.
- Linear and Circular Designs: Oughtred also designed circular slide rules, making the device more compact.
- Robert Bissaker’s Innovation: Robert Bissaker invented the familiar inner sliding rule in 1654.
Engineering and Drafting Scales:
- Scale Drawings: Scale drawings represent objects at a reduced size, making it easier to handle large or detailed items on paper.
- Engineering Blueprints: Scale rules are used to measure and create blueprints and technical drawings.
- Scales for Specific Applications: Engineering scales are divided into specific fractions, like tenths, twentieths, etc., of an inch, allowing for accurate measurements in various engineering applications.
Modern Uses:
- Surveying and Mapping: Scale rules continue to be used in surveying and map-making, where accurate representation of distances is crucial.
- Architecture and Construction: Architects and construction professionals use scale rules to create blueprints and plans, ensuring accurate dimensions in the final product.
Sources of Information
Scales and Rules for Measuring and Plotting – images and details of examples through the ages.
Slide Ruler – Wikipedia
Designing Buildings – The Construction Wiki
Determine Dimensions from Drawings – Describes use of scale rulers to determine actual dimensions from drawings
How To Use Scale Rulers
Example suppliers: Building Link; Blundell Harling