The hertz is equivalent to cycles per second.[2] In defining the second, the CIPM declared that "the standard to be employed is the transition between the hyperfine levels F = 4, M = 0 and F = 3, M = 0 of the ground state 2S1/2 of the cesium 133 atom, unperturbed by external fields, and that the frequency of this transition is assigned the value 9 192 631 770 hertz"[3] thereby effectively defining the hertz and the second simultaneously.
In English, "hertz" is also used as the plural form.[4] As an SI unit, Hz can be prefixed; commonly used multiples are kHz (kilohertz, 103 Hz), MHz (megahertz, 106 Hz), GHz (gigahertz, 109 Hz) and THz (terahertz, 1012 Hz). One hertz simply means "one cycle per second" (typically that which is being counted is a complete cycle); 100 Hz means "one hundred cycles per second", and so on. The unit may be applied to any periodic event—for example, a clock might be said to tick at 1 Hz, or a human heart might be said to beat at 1.2 Hz. The "frequency" or activity of aperiodic or stochastic events, such as radioactive decay, is expressed in becquerels, not hertz.
Even though angular velocity, angular frequency and the unit hertz all have the dimension 1/s (reciprocal second), angular velocity and angular frequency are not expressed in hertz,[5] but rather in an appropriate angular unit such as radians per second. Thus a disc rotating at 60 revolutions per minute (rpm) is said to be rotating at either 2π rad/s or 1 Hz, where the former measures the angular velocity and the latter reflects the number of complete revolutions per second. The conversion between a frequency f measured in hertz and an angular velocity ω measured in radians per second is
and .
This SI unit is named after Heinrich Hertz. As with every International System of Units (SI) unit whose name is derived from the proper name of a person, the first letter of its symbol is upper case (Hz). However, when an SI unit is spelled out in English, it should always begin with a lower case letter (hertz), except in a situation where any word in that position would be capitalized, such as at the beginning of a sentence or in capitalized material such as a title. Note that "degree Celsius" conforms to this rule because the "d" is lowercase. —Based on The International System of Units, section 5.2.

Vibration[edit]
Sound is a traveling longitudinal wave which is an oscillation of pressure. Humans perceive frequency of sound waves as pitch. Each musical note corresponds to a particular frequency which can be measured in hertz. An infant's ear is able to perceive frequencies ranging from 20 Hz to 20,000 Hz; the average adult human can hear sounds between 20 Hz and 16,000 Hz.[7] The range of ultrasound, high-intensity infrasound and other physical vibrations such as molecular vibrations extends into the megahertz range and well beyond.
Electromagnetic radiation[edit]
Electromagnetic radiation is often described by its frequency—the number of oscillations of the perpendicular electric and magnetic fields per second—expressed in hertz.
Radio frequency radiation is usually measured in kilohertz (kHz), megahertz (MHz), or gigahertz (GHz). Light is electromagnetic radiation that is even higher in frequency, and has frequencies in the range of tens (infrared) to thousands (ultraviolet) of terahertz. Electromagnetic radiation with frequencies in the low terahertz range, (intermediate between those of the highest normally usable radio frequencies and long-wave infrared light), is often called terahertz radiation. Even higher frequencies exist, such as that of gamma rays, which can be measured in exahertz. (For historical reasons, the frequencies of light and higher frequency electromagnetic radiation are more commonly specified in terms of their wavelengths or photon energies: for a more detailed treatment of this and the above frequency ranges, see electromagnetic spectrum.)
Computing[edit]
In computing, most central processing units (CPU) are labeled in terms of their clock rate expressed in megahertz or gigahertz (106 or 109 hertz, respectively). This number refers to the frequency of the CPU's master clock signal ("clock rate"). This signal is a square wave, which is an electrical voltage that switches between low and high values at regular intervals. Hertz has become the primary unit of measurement accepted by the general populace to determine the performance of a CPU, but many experts have criticized this approach, which they claim is an easily manipulable benchmark.[8] For home-based personal computers, CPU clock speeds have ranged from approximately 1 megahertz in the late 1970s (Atari, Commodore, Apple computers) to up to 6 GHz in IBM POWER processors.
Various computer buses, such as the front-side bus connecting the CPU and northbridge, also operate at various frequencies in the megahertz range.

Malaysia–Singapore Second Link (Malay: Laluan Kedua Malaysia–Singapura), is a bridge connecting Singapore and Johor, Malaysia. In Singapore, it is officially known as the Tuas Second Link. The bridge was built to reduce the traffic congestion at the Johor–Singapore Causeway, and was opened to traffic on 2 January 1998. It was officially opened by Singapore's then Prime Minister Goh Chok Tong with his counterpart, Dr Mahathir Mohamed, who was then Prime Minister of Malaysia. The bridge supports a dual-three lane carriageway linking Kampong Ladang at Tanjung Kupang, Johor to Jalan Ahmad Ibrahim at Tuas, Singapore. The total length of the bridge over water is 1,920 m (6,300 ft).
At Malaysian side, the bridge is connected to the Second Link Expressway (E3) (Malay: Lebuhraya Laluan Kedua Malaysia-Singapura) also known as Linkedua Expressway, which links from Senai North Interchange (exit 253) at North-South Expressway, Senai Airport and Taman Perling, Johor Bahru via its extension known as Johor Bahru Parkway. In Singapore, the bridge connects to the Ayer Rajah Expressway.
The checkpoint on Malaysia side is called the Sultan Abu Bakar CIQ Complex. The checkpoint on Singapore side, the Tuas Checkpoint, was built on 19.6 ha (47.4 acres) of reclaimed land at a cost of S$485 million. Designed by CPG Corporation, it involved the use of 54,000 cubic metres of concrete and 18,000 tones of reinforcing steel, and won the Architectural Design Award and Best Buildable Design Award awarded by the Singapore Institute of Architects and the Building and Construction Authority respectively [1].
Usually, traveling along the second link is much faster than traveling on the Causeway, as the traffic is smoother in both directions. However, during festive periods (especially Chinese New Year, Hari Raya, Christmas and Deepavali), the huge amount of traffic going between Malaysia and Singapore still leads to massive jams on both the causeway and the second link.

A Validation Master Plan, also referred to as "VMP", outlines the principles involved in the qualification of a facility, defining the areas and systems to be validated, and provides a written program for achieving and maintaining a qualified facility. A VMP is the foundation for the validation program and should include process validation, facility and utility qualification and validation, equipment qualification, cleaning and computer validation. It is a key document in the GMP (Good manufacturing practice) regulated pharmaceutical industry as it drives a structured approach to validation projects.
Food and Drug Administration inspectors often look at VMPs during audits to see whether or not a facility's validation strategy is well thought-out and organized. A VMP should have logical reasoning for including or excluding every system associated with a validation project based on a risk assessment.
Common topics to be covered in a Validation Master Plan: Introduction, scope, responsibilities, description of facility and design, building and plant Layout, cleanrooms and associated controlled environments, storage areas, personnel, personnel and material Flow, water and solid waste handling, infrastructure and utilities, water system, ventilation and air-conditioning system, clean steam, compressed air, gases and vacuum system, list manufacturing equipment, building management systems, products that are planned to be validated, qualification/validation approach, process validation and cleaning validation approach, microbiological monitoring, computer Validation, calibration, maintenance, related SOPs.