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SI brochure, Table 6 ( Section 4.1)

Table 6. NonSI units accepted for use with the International System of Units

Quantity 
Name of unit 
Symbol for unit 
Value in SI units 

time 
minute 
min 
1 min = 60 s 
hour ^{(a)} 
h 
1 h = 60 min = 3600 s 
day 
d 
1 d = 24 h = 86 400 s 
plane angle 
degree ^{(b,c)} 
° 
1° = (/180) rad 
minute 
' 
1' = (1/60)° = (/10 800) rad 
second ^{(d)} 
'' 
1'' = (1/60)' = (/648 000) rad 
area 
hectare ^{(e)} 
ha 
1 ha = 1 hm^{2} = 10^{4} m^{2} 
volume 
litre ^{(f)} 
L, l 
1 L = 1 l = 1 dm^{3} = 10^{3} cm^{3} = 10^{–3} m^{3} 
mass 
tonne ^{(g)} 
t 
1 t = 10^{3} kg 
(a) 
The symbol of this unit is included in Resolution 7 of the 9th CGPM (1948). 
(b) 
ISO 31 recommends that the degree be divided decimally rather than using the minute and the second. For navigation and surveying, however, the minute has the advantage that one minute of latitude on the surface of the Earth corresponds (approximately) to one nautical mile. 
(c) 
The gon (or grad, where grad is an alternative name for the gon) is an alternative unit of plane angle to the degree, defined as (/200) rad. Thus there are 100 gon in a right angle. The potential value of the gon in navigation is that because the distance from the pole to the equator of the Earth is approximately 10 000 km, 1 km on the surface of the Earth subtends an angle of one centigon at the centre of the Earth. However the gon is rarely used. 
(d) 
For applications in astronomy, small angles are measured in arcseconds (i.e. seconds of plane angle), denoted as or '', milliarcseconds, microarcseconds, and picoarcseconds, denoted mas, µas, and pas, respectively, where arcsecond is an alternative name for second of plane angle. 
(e) 
The unit hectare, and its symbol ha, were adopted by the CIPM in 1879 (PV, 1879, 41). The hectare is used to express land area. 
(f) 
The litre, and the symbol lowercase l, were adopted by the CIPM in 1879 (PV, 1879, 41). The alternative symbol, capital L, was adopted by the 16th CGPM (1979, Resolution 6) in order to avoid the risk of confusion between the letter l (el) and the numeral 1 (one). 
(g) 
The tonne, and its symbol t, were adopted by the CIPM in 1879 (PV, 1879, 41). In English speaking countries this unit is usually called "metric ton". 








