Precision Measurement: Instruments and Unit Systems Explained

Measuring Instruments: Definition and Features

A measuring instrument is a device designed to be used to make measurements, either alone or in conjunction with ancillary equipment.

For proper use, the key features of a measuring instrument to be aware of are:

1. Graduated System

   This system will have its divisions. If the tenth division is a number, it indicates the metric system, where each division is 1 mm. Otherwise, it is the English system.

   Figure 1.2: Metric Ruler

2. Range

   The range of a measuring instrument is the field between the minimum and maximum values that can be measured.

   Figure 1.4: Range of a Ruler and a Micrometer

3. Degree of Accuracy or Reading

   This refers to the value of the minimum, exact subdivision that can be read on the instrument.

   Figure 1.5: Degree of Precision of a Ruler

Unit Systems

A unit system is a set of interrelated units that are fixed and determined.

Systems of units commonly used in industrial and fishing operations in our country include the English system, the Metric system, and the International System of Units (SI).

English System

In the English system, the unit of length commonly used in workshops is the inch, which has sub-multiple fractions and decimals.

1. Ruler with Fractional Inch Submultiples

   (e.g., 1/8" on top and 1/16" for each division below).

   Figure 2.1: Common Fractional Inch Ruler

2. Ruler with Decimal Inch Submultiples

   (e.g., 0.025" for each division).

   Figure 2.2: Decimal Inch Foot Rule

Metric System

The Metric System is based on the meter. It is a decimal system, meaning each unit is contained ten times in the unit immediately above it and contains ten times the unit immediately below it. For example, one centimeter is contained 10 times in a decimeter and contains 10 millimeters.

The International System of Units (SI)

The International System of Units (SI) aims to:

• Have a unique and practical system of units for weights and measures that is internationally understandable.
• Avoid continuous conversion from one unit system to another.
• Avoid mistakes.
• Avoid the use of complicated factors other than unity.

It primarily consists of basic, derived, and supplementary units. The basic units are: