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SI brochure, from section 4.2

Name 
Symbol 
Value in SI units 

curie ^{(a)} 
Ci 
1 Ci = 3.7 x 10^{10} Bq 
röntgen ^{(b)} 
R 
1 R = 2.58 x 10^{–4} C/kg 
rad ^{(c, f)} 
rad 
1 rad = 1 cGy = 10^{–2} Gy 
rem ^{(d, f)} 
rem 
1 rem = 1 cSv = 10^{–2} Sv 
X unit ^{(e)} 

1 X unit 1.002 x 10^{–4} nm 
gamma ^{(f)} 

1 = 1 nT = 10^{–9} T 
jansky 
Jy 
1 Jy = 10^{–26} W · m^{–2} · Hz^{–1} 
fermi ^{(f)} 

1 fermi = 1 fm = 10^{–15} m 
metric carat ^{(g)} 

1 metric carat = 200 mg = 2 x 10^{–4} kg 
torr 
Torr 
1 Torr = (101 325/760) Pa 
standard atmosphere 
atm ^{(h)} 
1 atm = 101 325 Pa 
calorie 
cal 
^{(i)} 
micron ^{(f)} 
µ ^{(j)} 
1 µ = 1 µm = 10^{–6} m 

(a) The curie is a special unit employed in nuclear physics to express activity of radionuclides (12th CGPM, 1964, Resolution 7).
(b) The röntgen is a special unit employed to express exposure to x or radiation.
(c) The rad is a special unit employed to express absorbed dose of ionizing radiation. When there is risk of confusion with the symbol for radian, rd may be used as the symbol for rad.
(d) The rem is a special unit used in radioprotection to express dose equivalent.
(e) The X unit was employed to express the wavelengths of x rays. Its relationship with the SI unit is an approximate one.
(f) Note that this nonSI unit is exactly equivalent to an SI unit with an appropriate prefix.
(g) The metric carat was adopted by the 4th CGPM in 1907 (CR, 8991) for commercial dealings in diamonds, pearls and precious stones.
(h) Resolution 4 of the 10th CGPM (1954). The designation "standard atmosphere" for a reference pressure of 101 325 Pa is still acceptable.
(i) Several "calories" have been in use:
a calorie labelled "at 15 °C": 1 cal_{15} = 4.1855 J (value adopted by the CIPM in 1950; PV, 1950, 22, 7980);
a calorie labelled "IT" (International Table): 1 cal_{IT} = 4.1868 J (5th International Conference on the Properties of Steam, London, 1956);
a calorie labelled "thermochemical": 1 cal_{th} = 4.184 J.
(j) The micron and its symbol, adopted by the CIPM in 1879 (PV, 1879, 41) and repeated in Resolution 7 of the 9th CGPM (1948) were abolished by the 13th CGPM (19671968), Resolution 7).









