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Units of measure1 - now let's try to get this right

Hintlink - Units of measure
Units  | Prefixes  | Base Units  | Derived Units  | Mistakes  | Uses  | Dislikes  | Oddities  | Footnotes

Specifying a quantity is a three-part 'thing'  -  Number, Prefix (or multiplier) PLUS the unit being used

First, let's deal with the prefixes
IMPORTANT! All prefixes are in lower case, working from the smallest. When the lower case version has been used, ONLY THEN is the upper-case version used
yotta Y 1024 Extremely large
zetta Z 1021
exa E 1018
peta P 1015
tera T 1012
giga G 109
mega M 106
kilo k 103
hecto h 102
deca da 101
-
-
100  (=1)
-
deci d 10-1
centi c 10-2
milli m 10-3
micro 10-6
nano n 10-9
pico p 10-12
femto f 10-15
atto a 10-18
zepto z 10-21
yocto y 10-24 Extremely small


Hintlink - Units of measure
Units  | Prefixes  | Base Units  | Derived Units  | Mistakes  | Uses  | Dislikes  | Oddities  | Footnotes

Now the fundemental (base) units upon which everything is built
IMPORTANT! Units which are named after real scientists begin in UPPER CASE, all others are in lower case.
Name Symbol Measure Named After
metre m length
kilogram[*] kg mass
second s time
ampere A electric current Ampre
kelvin K thermodynamic temperature Kelvin
mole mol amount of substance
candela cd luminous intensity
* The kilogram is an unusual exception as it is based on the mass of a small squat cylinder of ~47 cubic centimetres of platinum-iridium alloy kept in a laboratory in France (near Paris). The gram is far  too small to reliably measure, so the kilogram is used. The standard is rarely examined and cannot be touched or knocked, so as not to change the mass.
There are plans to somehow provide a better standard, but it has defied physicists, so far.

Hintlink - Units of measure
Units  | Prefixes  | Base Units  | Derived Units  | Mistakes  | Uses  | Dislikes  | Oddities  | Footnotes

Some of the derived units
IMPORTANT! Units which are named after real scientists begin in UPPER CASE, all others are in lower case.
Name Symbol Quantity Named After
hertz Hz frequency Hertz
radian rad angle (dimensionless)

steradian sr solid angle (dimensionless)

newton N force, weight Newton
pascal Pa pressure, stress Pascal
joule J energy, work, heat Joule
watt W power, radiant flux Watt
coulomb C electric charge or quantity of electricity Coulomb
volt V voltage, electrical potential difference, electromotive force Volta
farad F electrical capacitance Faraday
ohm[*] Ω electrical resistance, impedance, reactance Ohm
siemens S electrical conductance Siemens
weber Wb magnetic flux Weber
tesla T magnetic field strength, magnetic flux density Tesla
henry H electrical inductance Henry
degree Celsius C temperature relative to 273.15 K Celsius
lumen lm luminous flux
lux lx illuminance
becquerel Bq radioactivity (decays per unit time) Becquerel
gray Gy absorbed dose (of ionizing radiation) Gray
sievert Sv equivalent dose (of ionizing radiation) Sievert
katal kat catalytic activity
bel
B
ratio of values
Bell
* The ohm is an exception, being abbreviated to Ω rather than O (to save confusion with 0).
Dr. Georg Simon Ohm did, of course, exist, as in Ohm's Law.


Hintlink - Units of measure
Units  | Prefixes  | Base Units  | Derived Units  | Mistakes  | Uses  | Dislikes  | Oddities  | Footnotes

Common mistakes
KHz
You mean kHz
khz
You mean kHz
meter
You mean metre
liter*
You mean litre
mhz
You mean MHz
mL
You mean ml (there was no Mr./Dr. Litre). In Europe m is printed on products / packaging
MS
You mean ms, most likely, for milliseconds. megasiemens would be unusual
MG
You mean mg, for milligrams
MCG
You mean g
mil
You mean a millimetre, not 1/1000"
M
You mean m, metres. As in 20m or 160m (amateur radio bands)
CM
You mean cm, centimetres. As in 70cm or 23cm (amateur radio bands)
MF
You mean F
MMF
You mean pF
db or DB
You mean dB

undoubtedly more to follow :-)
A litre is not actually a unit recognised under SI definitions, but is in common usage.

Hintlink - Units of measure
Units  | Prefixes  | Base Units  | Derived Units  | Mistakes  | Uses  | Dislikes  | Oddities  | Footnotes

Common uses:
mil = millimetre
Angstrom (
), 10-10m (8 is about the size of an atom) - is used so as not to be confused with the ampere (A)
micron = 1m [FYI, resolution of best optical microscope ~2 microns]
mho, reciprocal of ohm. Same as siemen.
Resistance values (often) use the multiplier instead of the decimal point e.g. 1k2, 4M7 (often without the
Ω symbol)
[this has the added advantage of removing the decimal point '.', which in Continental Europe is a ',']
Capacitor values (often) use the last figure to indicate the 'power' of the value above 10pF e.g. 104 = 10(0000) = 100,000pF = 100nF = 0.1uF
dB = decibel. Have never seen bel used. Often used against a reference level dBm, dBV [an oddity, dBm refers to 'relative to 1mW']
fF do exist and I have made them using quartz pillared capacitors [low, sub pF capacitors can be made by using PTFE covered wire twisted together]

Hintlink - Units of measure
Units  | Prefixes  | Base Units  | Derived Units  | Mistakes  | Uses  | Dislikes  | Oddities  | Footnotes

Personal dislikes:
centimetre - an abomination of a measurement unit
Monetary system disobeys all reason ($1m, $1b, $1bn, $1T, etc.)

Hintlink - Units of measure
Units  | Prefixes  | Base Units  | Derived Units  | Mistakes  | Uses  | Dislikes  | Oddities  | Footnotes

Oddities:
VU (volume unit) is a completely arbitrary audio 'standard'.
Peak reading meters are much to be preferred [as used by my Nakamichi 482 cassette deck, utterly the best deck in the 1980s by far].

Further information, in detail, can be found at the SI Reference or these Wikipedia links:
Prefixes  Base Units Derived Units

Hintlink - Units of measure
Units  | Prefixes  | Base Units  | Derived Units  | Mistakes  | Uses  | Dislikes  | Oddities  | Footnotes

Examples
1)
I was finally driven to write this page by a catalog from a well known US vendor with 13 electronics outlets, no less!
On the front page, in glorious color, was printed: FT-891 HF + 50Mhz All Mode Mobile Transceiver with 100w Output.
Reading the rest of the catalog of 124 pages revealed hundreds of typographical and unit errors!
2) Advertising on well-known web page:
Only on the blue background banners How can you bear this on a $900 controller?   MHz also wrong on label on product(!) 80m !
 3) Please let manufacturers (and writers) know that they are making mistakes....

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