What are 'Standard International units'?

• Where are you from? Send us a postcard! Strange Attractor, c/ PO Box 9, Fitzroy, VIC 3065, Australia
• The seven Système International d'Unités (SI) base units: second, mole, metre, kilogram, kelvin, candela, ampere (National Physical Laboratory)
• The seven Système International d'Unités (SI) base units: second, mole, metre, kilogram, kelvin, candela, ampere (Wikipedia)
• The base units (Bureau International des Poids et Mesures)
• The SI system kicked off after 1799 (The National Institute of Standards & Technology)
• Moon Unit Zappa, child of Frank Zappa (Wikipedia)
• The 'cubit' was the length from the tip of one's middle finger to the bottom of the elbow (Wikipedia)
• History of length measurement: From cubits to lasers (National Physical Laboratory)
• A history of all the weird units of measurement from ye olde ancient times (Encyclopaedia Britannica)
• A history of the kilogram (National Physical Laboratory)
• Standard time was introduced from the mid-1800s around the world with the coming of the railways (Wikipedia)
• The Allegheny Observatory used to provide accurate time updates via telegraph in North America (Wikipedia)
• A history of timekeeping devices (Wikipedia)
• The second used to be defined as 1/86,400 of a day, but now it's "the duration of 9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the caesium-133 atom" (Wikipedia)
• A brief history of the second (The National Institute of Standards & Technology)
• "A new optical clock ticks so consistently that if it had started at the dawn of the universe, it would have lost less than two minutes" (The Independent)
• The strontium optical clock (OSA Publishing)
• Where are atomic clocks? They're everywhere now (HyperPhysics, Georgia State University)
• Clock synchronisation around the world is really important for computers & stuff (Wikipedia)
• International Atomic Time tells us at which speed our clocks should tick (Time and Date)
• What is needed to synchronise time across atomic clocks in the world? (Quora)
• How to improve time accuracy on iPhone & Apple Watch (iPhone Tricks)
• Security implications of the humble computer clock (Network World)
• Who invented the second? Claudius Ptolemy around 150 C.E. (Reference)
• Why is a minute divided into 60 seconds, an hour into 60 minutes, yet there are only 24 hours in a day? (Scientific American)
• The book Johnny was talking about by Dava Sobel: 'Longitude: The true story of a lone genius who solved the greatest scientific problem of his time' (Wikipedia)
• See John Harrison's original clocks in the museum at Greenwich, London (Royal Museums Greenwich)
• We had the second for ages, then the kelvin was first defined in 1743, the kilogram & metre followed in 1793, the amp in 1881, the mole in 1900, & the candela in 1946, but they've been refined now (Wikipedia)
• The metre was originally defined as one ten-millionth of the distance from the equator to the North Pole (Wikipedia)
• The metre is now defined as the distance travelled by light in 1/299,792,458th of a second (Wikipedia)
• A brief history of the metre (The National Institute of Standards & Technology)
• The speed of light: 299,792,458 metres per second (Encyclopaedia Britannica)
• People debating pool tolerance & why timing isn't more accurate in swimming (Reddit)
• Meet the kilogram - a.k.a 'La Grande K' or 'Big K' (Wikipedia)
• There did used to be someone who went around checking stuff - the 'city meter' - "checking both the weights of goods as sold & the accuracy of the metal weights used" (Hall Genealogy Website)
• The International Prototype Kilogram (IPK) & its copies - Australia has one (Wikipedia)
• If someone knocks a chunk off the IPK, the definition of a kilogram changes (Wikipedia)
• A list of the prefixes for metric units of measurement: e.g. 'kilo' just means a thousand (The National Institute of Standards and Technology)
• "The magnitude of many of the units comprising the SI system...are highly dependent upon the stability of a 137-year-old, golf-ball-sized cylinder of metal stored in a vault in France" (Wikipedia)
• The new kilogram is due out in 2018 - stay tuned (The National Institute of Standards and Technology)
• Redefining the kilogram: Mass, Planck & Einstein (The National Institute of Standards and Technology)
• Redefining the kilogram: The 'Watt balance' (The National Institute of Standards and Technology)
• After a fraught few years, experiments to redefine the kilogram have reached agreement (Nature)
• What is a mole? Not the burrowing kind with small eyes (The National Institute of Standards & Technology)
• Avogadro's number & the mole (Wikipedia)
• What is a mole & why are moles used? (About Education, Chemistry)
• Hello kelvin - this unit is 1/273.16 of the thermodynamic temperature of the triple point of water (The National Institute of Standards & Technology)
• What is the triple point of water? (Wikipedia)
• What is Celsius? (Wikipedia)
• Deep breath: "The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross section, & placed 1 metre apart in a vacuum, would produce between these conductors a force equal to 2 x 10-7 newton per metre of length" (The National Institute of Standards & Technology)
• What is the difference between voltage & current (amperes)? (The Charging Point)
• Everything you wanted to know about charging your iPhone or iPad (Apple, Communities)
• iPhone & iPad chargers appear to be around 1-2 amps according to this (Apple, Communities)
• I believe you now Johnny: Turns out the coloured rings for electric toothbrushes really are to tell family members' brush heads apart (Electric Teeth)
• Meet the candela, "the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency 540 x 1,012 hertz & that has a radiant intensity in that direction of 1/683 watts per steradian" (The National Institute of Standards & Technology)
• What is black body radiation? (Cosmos, Swinburne University)
• We can use luminous intensity to measure how far away stars are (Science, How Stuff Works)
• 'Intrinsic luminosity' is how bright something is & 'apparent brightness' is how bright it looks - knowing these details helps us measure how far away stars are (Department of Astronomy & Astrophysics, Penn State)
• Stellar brightness (Department of Astronomy, The Ohio State University)
• Brightness, luminosity & the magnitude scale (Department of Astronomy, Cornell University)
• What is a standard candle? (Cosmos, Swinburne University)
• (non SI) Units for quantities that describe biological effects (Bureau International des Poids et Mesures)
• The future - proposed redefinition of SI base units (Wikipedia)
• A more fundamental International System of units (Physics Today)

Corrections

• Sorry Johnny, you got latitude & longitude mixed up - latitude is north-south, longitude is east-west (Encyclopaedia Britannica)