The International System of Units, abbreviated as SI, is the most widely used system of measurement in the world. It is based on seven fundamental physical quantities, from which all others are derived.

Fundamental Quantities

The seven fundamental quantities and their respective units of measurement are:

• Length: measured in meters (m).
• Mass: measured in kilograms (kg).
• Time: measured in seconds (s).
• Electric current: measured in amperes (A).
• Thermodynamic temperature: measured in kelvins (K).
• Amount of substance: measured in moles (mol).
• Luminous intensity: measured in candelas (cd).

Derived Quantities

Derived quantities are obtained by combining fundamental quantities through mathematical operations such as products or ratios.

Below are some examples of derived quantities with updated practical applications:

1. Velocity (Length / Time):
   • The unit of measurement is meters per second ($m/s$).
   • Example: The movement speed of a robotic arm or the feed rate of a CNC machine tool.
2. Surface / Area (Length $\times$ Length):
   • The unit of measurement is the square meter ($m^2$).
   • Example: The contact surface area of a mechanical seal or the cross-section of a structural beam.
3. Volume (Length $\times$ Length $\times$ Length):
   • The unit of measurement is the cubic meter ($m^3$).
   • Example: The internal capacity of an industrial tank or the displacement of a hydraulic pump.

Standards

Technical standards are documents that define the characteristics (dimensions, performance, safety, etc.) of a product, process, or service, according to the state of the art and are recognized by an authorized body.

What are they for?

Standards are essential to ensure the quality, safety, and reliability of products. They facilitate international trade and ensure that products and services from different countries are compatible.

Standardization Bodies

Standards are developed by standardization bodies at national, European, and international levels:

• UNI: Ente Nazionale Italiano di Unificazione (Italy).
• CEN: European Committee for Standardization (Europe).
• ISO: International Organization for Standardization (World).

Types of Standards

Standards can be classified into different types based on their content:

• Fundamental standards: concern terminology, symbols, and general principles (e.g., symbols used in technical drawings).
• Terminology standards: define the terms used in a specific sector.
• Testing standards: describe the methods to be used to verify the characteristics of a product (e.g., procedures for laboratory calibration).
• Product standards: define the technical specifications of a product.

Importance in Metrology

In the field of metrology, standards are fundamental to ensure that measurements are accurate and comparable.

Practical Examples:

1. ISO 9001: This is a standard that defines the requirements for a quality management system. For a calibration laboratory, following this standard means ensuring consistent process control.
2. ISO/IEC 17025: This standard specifies the general requirements for the competence of testing and calibration laboratories. It ensures that a metrology lab produces technically valid results.
3. UNI EN ISO 10360: A specific standard used for the acceptance and verification of Coordinate Measuring Machines (CMM).