© Museum of the History of Science, Oxford

This object is a simple type of mathematical instrument used for measuring, called a gauge. Gauges are tools used to measure sizes and volumes of real things like pieces of wood or barrels. They are always very simple because they are used by people doing real practical jobs. They therefore need to be easy to use and not to have any unnecessary or confusing scales or numbers on them.
Gauges are a very simple application of mathematics but they are still important. We use mathematics all the time in our lives to do all sorts of different things, although we often forget this. For example, when you go to a shoe shop to buy new shoes your feet are always measured first. Measuring is a mathematical operation. The measuring is done with a gauge that tells the shop assistant what size of shoes you need. All gauges are created by mathematical principles.
No one really knows what this gauge was used to measure but it could have been used for measuring the width of pieces of wood. It has two endstops that the thing to be measured would be placed against and a scale off which to read the measurement. The scale is labelled with numbers from 1 to 19.
This gauge was made in an Islamic country. Because of this all the writing on it is in Arabic script. The numbers for the scale are written in a system called 'abjad' numerals. In the abjad number system, numbers are written as letters. The name of the system of abjad numerals derives from the first four letters used for these numerals, a=1, b=2, j=3, and d=4. For numbers above 10, letters can be joined together, although there are specific single letters for tens and hundreds etc. For example, 15 is written as 'y' (representing 10) and 'h' (representing 5) joined together. Numbers written in the abjad system can be hard for us to read now but were used a lot in Islamic mathematics.