I've had an interest in dimensional analysis (ie what units or "dimensions" one should use to measure various things) ever since an article on it back in Analog in the mid 60s.
It also suggested some base units to derive things from, which does drag in metrology.
The suggested units were based on the mass of the electron, the speed of light, and a few other things.
As I recall the only measurement currently based on a physical standard is the kilogram. Length is now based on wavelengths of light generated by a specific quantum transition in s specific isotope. And the speed of light is now a defined constant, so time is derived from the definition of length & the speed of light.
Or I may have that backwards.
Current is the weird one, with the ampere having a truly bizarre (but more or less reproducible) definition, with the Coulumb (unit of charge) derived from that and the time definition.
Odd factiod: The US gallon is apparently legally *defined* as 231 cubic inches. And the inch is defined as 2.54 cm.
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timeasmymeasure
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Date: 2013-02-23 12:23 am (UTC)It also suggested some base units to derive things from, which does drag in metrology.
The suggested units were based on the mass of the electron, the speed of light, and a few other things.
As I recall the only measurement currently based on a physical standard is the kilogram. Length is now based on wavelengths of light generated by a specific quantum transition in s specific isotope. And the speed of light is now a defined constant, so time is derived from the definition of length & the speed of light.
Or I may have that backwards.
Current is the weird one, with the ampere having a truly bizarre (but more or less reproducible) definition, with the Coulumb (unit of charge) derived from that and the time definition.
Odd factiod: The US gallon is apparently legally *defined* as 231 cubic inches. And the inch is defined as 2.54 cm.