1.4142 - The diagonal (approximate, to four decimal places) of a 1 x 1 square, also known as Pythagoras's Constant, and therefore also the ratio (1:1.4142) for calculating the diagonal side of a right-angled triangle in which the two short sides are of equal length.
 
1.6180 - The Golden Number (to four decimal places). Also known as the Golden Section, Divine Proportion, and phi (pronounced 'fy' as in the word 'fly') the twenty-first letter of the Greek alphabet. Also loosely referred to as Golden Ratio (1:1.618). Phi is used intentionally or instinctively in many different areas of design, for example architecture, music, and art. Phi is also an easy 'secret' to achieving aesthetically pleasing positioning and proportions. The Golden Ratio is found in diverse designs such as Stradivarius violins, the Pyramids, Notre Dame Cathedral, and in nature, for example the human face.
 
3.14159 - Pi, normally represented by the Greek letter pi (P) symbol p. Pi is typically used for calculating the area (p x radius squared) or circumference (p x diameter) of a circle. Pi has an infinite number of decimal places, and fascinates mathematicians in calculating pi itself, and memory experts too in memorizing as much of it as possible.
 
4/4 - Four beats to the bar, the most common rhythm in music.
 
10:10 - A UK environmental campaign that asks businesses, organisations and individuals to cut their carbon emissions by 10% in the year 2010.
 
13 - The most superstitious number, 13 affects business in surprising ways through absenteeism, cancellations, and design. Western airlines, for example, tend not to have seats and rows numbered 13. Friday 13th is a particularly superstitious date. Friday and the number 13 derive their superstitious reputations mostly from Christian beliefs and Norse folklore.
 
21-Gun Salute - Traditional honour given to royalty and heads of state, derived from the old signal of peaceful intent, when multiple firing practically removed capability for immediate threat due to re-loading time.
 
24-Carat/Karat - The purest form of gold (karat is US-English spelling, too soft for jewellery, hence gold jewellery is made of 22-carat, 18-carat, or 9-carat gold, etc., in which other metals such as copper are mixed. Carat is a measure of purity in which 24 parts equate (virtually) to 100% gold. 18-carat is therefore 75% gold. Less than 10-carat gold is generally not sold as gold. The carat measure of diamonds is different, for which carat is a measure of weight (1 carat = 200mg).
 
24-hour Society - Refers to a way of life available to many in the modern world in which people can work socialize, shop, bank, etc., 24 hours a day. The phenomenon has caused significant new thinking in business, management, marketing, etc., and continues to do so.
 
24/7 - Twenty four hours a day, seven days a week.
 
38 Ways of Persuasion - The classic semi-serious guide to winning arguments featuring in The Art of Always Being Right, by German philosopher Arthur Schopenhauer (1788-1860).
 
64,000 dollar/pound question - The key or crucial question in a particular issue, deriving from an old US TV gameshow called Take It Or Leave It, in which $64 was the top prize (it was an old old show..) Recently the expression commonly increases the sum to 64-million, to keep pace with inflationary values.
 
72 Rule - More commonly known as the Rule of 72, with variations 69 and 70, these are standard figures used by financial folk in calculating quickly the years required for an investment to double (or to halve) at a given interest rate. Typically 72 is divided by the compound interest rate to give the approximate years. 72 is more popular than 69 or 70 because it is quite reliable and easily divisible quickly by lots of different numbers.
 
80/20 Rule - The theory that 20% of effort produces 80% of results, and very many similar effects; also known as Pareto Rule or Pareto Principle, after its originator.
 
86 - 'Secret' code used by restaurant and bar staff when refusing service or ejecting a customer from the premises, and more recently referring to a menu item not available, which is sometimes a lie to achieve the first meaning. The term has existed since the early 1900s and no-one knows the true derivation, although increasingly daft ones are suggested.
 
360 Degree Thinking - A term used for considering all options in business, etc., as opposed to having narrow field vision.
 
360 Degree Feedback - An appraisal method typically entailing feedback about a manager given by fellow workers. See appraisals.