Primary elements are elements that originate from air and water. It comprises carbon, hydrogen and oxygen. Other primary elements are phosphorus, potassium and nitrogen. Secondary and tertiary elements contain sulfur, magnesium and calcium.

A device that measures (senses) a physical condition or variable of interest. Floats and thermocouples are examples of primary elements. Also called a sensor. The hydraulic structure used to measure flows.

A primary element is a sensor or detector that responds quantitatively to the measured variable and performs the initial measurement operation. A primary element performs the initial conversion of measurement energy.

Typically the question of primary elements comes from biology and usually from the aspects of genetics. Therefore the primary elements would carbon, hydrogen, oxygen, nitrogen and phosphorus.

Mendeleev discovered the periodic table (or Periodic System, as he called it) while attempting to organise the elements in February of 1869.

The Four Elements. Greek philosophy supposed the Universe to comprise four elements: Fire, Water, Earth, and Air.

An acronym derived from the words 'parts per million' (ppm) – a unit which means one particle of a given substance for 999,999 other particles, i.e., one part per million. The unit usually indicates the concentration of carbon dioxide in the air. See the carbon dioxide sensors.

(Or sensor.) The component of an instrument that converts an input signal into a quantity that is measured by another part of the instrument.

Each instrumentation system therefore usually consists of four constituent parts, the sensor, analogue signal processing circuits, an analogue-to- digital converter and a digital processor.

Examples of primary instruments include stocks, bonds, and currency, among others. Any spot market that trades the 'cash' asset involves a primary instrument. By contrast, the price of derivative instruments, such as options and futures, is often based on the value of a primary instrument.

Elements are divided into four major categories:

• Metals.
• Non-metals.
• Metalloids.
• Noble gases.

Since 2002, the IUPAC Inorganic Chemistry Division has been the official body responsible with assigning official names to new elements, with the IUPAC Council making the final decision.