Before we start talking about the different types of Scale Rules we should explain what a Scale Rule is and what it does. We have all used a rule, or ruler, at school to draw straight lines and to measure lines on drawings, or measurements as part of our geometry lessons. The basic ruler we used at school has a scale of one to one or 1:1, this means that if something is one unit in length the reading on the ruler will show that length. For example if a line is 25mm long the reading on the ruler will be 25mm.

The is fine for measuring a drawing that is drawn full size (1:1), but what we are drawing something that is too big to fit on the paper, such as the plans of a house or a large bridge? We then need to draw it to a smaller scale so that the object looks to have the correct proportions. For example, if we were drawing the plans for a new house we might use a scale of 1:50, so that for every 1000mm that the house measures, we only require a length of 20mm on the drawing, 1000 divided by 50.

If we were drawing a machine part we might draw it in half scale or 1:2, or a large bridge may be drawn at a much smaller scale of 1:200. This is where the Scale Rule helps us. As well as having a 1:1 scale on one of it’s edges , the scale rule has other scales on the other edges, it may have 1:10 on one edge, 1:50 on another and 1:200 on the forth face.

Typically a conventional flat or oval scale rule will have two scales on each face, for example 1:5 and 1:50 can be on the same face and the user decides which scale he or she needs to read. After a bit of practice it becomes a very easy task to identify and read each scale.

So what are the different types of Scale Rules? As with the origins of the traditional wooden school ruler, the early scale rules were of a similar material and appearance. The difference was that instead of just 1:1 scales the edges of the rule had different scales, sometimes just on the one side but often with other scales or conversion charts on the reverse side.

As we moved into the age of plastics, Scale Rules became more refined and more accurate, the lines forming the graduations could be finer and the indexing improved to show very accurate calibrations. The shapes also became more practical, Oval Scale Rules, as we know them today, were seen as an advancement as the face being used could be raised above the drawing giving less chance of ink smudges and dirty marks, style also plays a big part.

Triangular Scale Rules are a popular option, the section is more of a three pointed star shape which allows for six faces on which to put scales, this design therefore has the capacity to have up to twelve scales, a very practical tool. Because of it’s three dimensional shape the Triangular Scale Rule is easier to pick up and also easier to locate on a desk often covered with drawings!

There are also various types of extruded aluminium Rulers, flat aluminium and Stainless Steel Rules which all have their benefits depending on where they are to be used.