DD IEC/TS 61994-4-3:2008

Frequency - A term used to describe how often something is done

Frequency - A wave frequency is the number of times a wave repeats within a given time

Crystal - A solid substance that has symmetrically carved plane faces and can be regularly found in jewellery.

Crystal - A solid clear substance with many surfaces that glisten, commonly used in jewellery

Crystal - A solid substance with symmetrically arranged planes, commonly found in jewellery.

Vocabulary - The collaboration of words used in a language.

The British Standards Institution are a non profit making organisation, who produce standards and standard related services, for a variety of industries. The standards that they produce are used as a guideline or definition of the minimum levels certain services and product should reach. The standards are produced by BSI directly, following consultations and public enquiries. At shop.bsigroup.com, you can purchase a variety of standards. They stock documents for industries such as food and drink, engineering, building and construction, energy and utilities, transport and agriculture and farming. If you become a member of their site you can get huge discounts on their standards. They also offer training courses and conferences via their website, or you could take advantage of their online standards tools.