C | Useful Information

C | Useful Information

This appendix is broken into several tables.

Symbol Meaning Best Value Approximate Value
c c size 12{c} {} Speed of light in vacuum 2 . 99792458 × 10 8 m / s 2 . 99792458 × 10 8 m / s size 12{2 "." "99792458" times "10" rSup { size 8{8} } ` {m} slash {s} } {} 3 . 00 × 10 8 m / s 3 . 00 × 10 8 m / s size 12{3 "." "00" times "10" rSup { size 8{8} } ` {m} slash {s} } {}
G G size 12{G} {} Gravitational constant 6 . 67408 ( 31 ) × 10 11 N m 2 / kg 2 6 . 67408 ( 31 ) × 10 11 N m 2 / kg 2 size 12{6 "." "67384" \( "80" \) times "10" rSup { size 8{ - "11"} } ` {N cdot m rSup { size 8{2} } } slash {"kg" rSup { size 8{2} } } } {} 6 . 67 × 10 11 N m 2 / kg 2 6 . 67 × 10 11 N m 2 / kg 2 size 12{6 "." "67" times "10" rSup { size 8{ - "11"} } ` {N cdot m rSup { size 8{2} } } slash {"kg" rSup { size 8{2} } } } {}
N A N A size 12{N rSub { size 8{A} } } {} Avogadro’s number 6 . 02214129 ( 27 ) × 10 23 6 . 02214129 ( 27 ) × 10 23 size 12{6 "." "02214129" \( "27" \) times "10" rSup { size 8{"23"} } } {} 6 . 02 × 10 23 6 . 02 × 10 23 size 12{6 "." "02" times "10" rSup { size 8{"23"} } } {}
k k size 12{k} {} Boltzmann’s constant 1 . 3806488 ( 13 ) × 10 23 J / K 1 . 3806488 ( 13 ) × 10 23 J / K size 12{1 "." "3806488" \( "13" \) times "10" rSup { size 8{ - "23"} } ` {J} slash {K} } {} 1 . 38 × 10 23 J / K 1 . 38 × 10 23 J / K size 12{1 "." "38" times "10" rSup { size 8{ - "23"} } ` {J} slash {K} } {}
R R size 12{R} {} Gas constant 8 . 3144621 ( 75 ) J / mol K 8 . 3144621 ( 75 ) J / mol K size 12{8 "." "3144621" \( "75" \) ` {J} slash {"mol" cdot K} } {} 8 . 31 J / mol K = 1 . 99 cal / mol K = 0 . 0821 atm L / mol K 8 . 31 J / mol K = 1 . 99 cal / mol K = 0 . 0821 atm L / mol K size 12{8 "." "31"` {J} slash {"mol" cdot K=1 "." "99"` {"cal"} slash {"mol" cdot K=0 "." "0821"` {"atm" cdot L} slash {"mol" cdot K} } } } {}
σ σ size 12{σ} {} Stefan-Boltzmann constant 5 . 670373 ( 21 ) × 10 8 W / m 2 K 5 . 670373 ( 21 ) × 10 8 W / m 2 K size 12{5 "." "670373" \( "21" \) times "10" rSup { size 8{ - 8} } ` {W} slash {m rSup { size 8{2} } cdot K} } {} 5 . 67 × 10 8 W / m 2 K 5 . 67 × 10 8 W / m 2 K size 12{5 "." "67" times "10" rSup { size 8{ - 8} } ` {W} slash {m rSup { size 8{2} } cdot K} } {}
k k size 12{k} {} Coulomb force constant 8 . 987551788 . . . × 10 9 N m 2 / C 2 8 . 987551788 . . . × 10 9 N m 2 / C 2 size 12{8 "." "987551788" "." "." "." `` times "10" rSup { size 8{9} } ` {N cdot m rSup { size 8{2} } } slash {C rSup { size 8{2} } } } {} 8.99 × 10 9 N m 2 / C 2 8.99 × 10 9 N m 2 / C 2 size 12{9 times "10" rSup { size 8{9} } ` {N cdot m rSup { size 8{2} } } slash {C rSup { size 8{2} } } } {}
q e q e size 12{q rSub { size 8{e} } } {} Charge on electron 1 . 602176565 ( 35 ) × 10 19 C 1 . 602176565 ( 35 ) × 10 19 C size 12{ - 1 "." "602176565" \( "35" \) times "10" rSup { size 8{ - "19"} } `C} {} 1 . 60 × 10 19 C 1 . 60 × 10 19 C size 12{ - 1 "." "60" times "10" rSup { size 8{ - "19"} } `C} {}
ε 0 ε 0 size 12{ε rSub { size 8{0} } } {} Permittivity of free space 8 . 854187817 . . . × 10 12 C 2 / N m 2 8 . 854187817 . . . × 10 12 C 2 / N m 2 size 12{8 "." "854187817" "." "." "." `` times "10" rSup { size 8{ - "12"} } ` {C rSup { size 8{2} } } slash {N cdot m rSup { size 8{2} } } } {} 8 . 85 × 10 12 C 2 / N m 2 8 . 85 × 10 12 C 2 / N m 2 size 12{8 "." "85" times "10" rSup { size 8{ - "12"} } ` {C rSup { size 8{2} } } slash {N cdot m rSup { size 8{2} } } } {}
μ 0 μ 0 size 12{μ rSub { size 8{0} } } {} Permeability of free space × 10 7 T m / A × 10 7 T m / A size 12{4π times "10" rSup { size 8{ - 7} } ` {T cdot m} slash {A} } {} 1 . 26 × 10 6 T m / A 1 . 26 × 10 6 T m / A size 12{1 "." "26" times "10" rSup { size 8{ - 6} } ` {T cdot m} slash {A} } {}
h h size 12{h} {} Planck’s constant 6 . 62606957 ( 29 ) × 10 34 J s 6 . 62606957 ( 29 ) × 10 34 J s size 12{6 "." "62606957" \( "29" \) times "10" rSup { size 8{ - "34"} } `J cdot s} {} 6 . 63 × 10 34 J s 6 . 63 × 10 34 J s size 12{6 "." "63" times "10" rSup { size 8{ - "34"} } `J cdot s} {}
Table C1

Important Constants1

Symbol Meaning Best Value Approximate Value
m e m e size 12{m rSub { size 8{e} } } {} Electron mass 9 . 10938291 ( 40 ) × 10 31 kg 9 . 10938291 ( 40 ) × 10 31 kg size 12{9 "." "10938291" \( "40" \) times "10" rSup { size 8{ - "31"} } `"kg"} {} 9 . 11 × 10 31 kg 9 . 11 × 10 31 kg size 12{9 "." "11" times "10" rSup { size 8{ - "31"} } `"kg"} {}
m p m p size 12{m rSub { size 8{p} } } {} Proton mass 1 . 672621777 ( 74 ) × 10 27 kg 1 . 672621777 ( 74 ) × 10 27 kg size 12{1 "." "672621777" \( "74" \) times "10" rSup { size 8{ - "27"} } `"kg"} {} 1 . 6726 × 10 27 kg 1 . 6726 × 10 27 kg size 12{1 "." "6726" times "10" rSup { size 8{ - "27"} } `"kg"} {}
m n m n size 12{m rSub { size 8{n} } } {} Neutron mass 1 . 674927351 ( 74 ) × 10 27 kg 1 . 674927351 ( 74 ) × 10 27 kg size 12{1 "." "674927351" \( "74" \) times "10" rSup { size 8{ - "27"} } `"kg"} {} 1 . 6749 × 10 27 kg 1 . 6749 × 10 27 kg size 12{1 "." "6749" times "10" rSup { size 8{ - "27"} } `"kg"} {}
u u size 12{u} {} Atomic mass unit 1 . 660538921 ( 73 ) × 10 27 kg 1 . 660538921 ( 73 ) × 10 27 kg size 12{1 "." "660538921" \( "73" \) times "10" rSup { size 8{ - "27"} } `"kg"} {} 1 . 6605 × 10 27 kg 1 . 6605 × 10 27 kg size 12{1 "." "6605" times "10" rSup { size 8{ - "27"} } `"kg"} {}
Table C2

Submicroscopic Masses2

Sun mass 1 . 99 × 10 30 kg 1 . 99 × 10 30 kg size 12{1 "." "99" times "10" rSup { size 8{"30"} } `"kg"} {}
average radius 6 . 96 × 10 8 m 6 . 96 × 10 8 m size 12{6 "." "96" times "10" rSup { size 8{8} } `m} {}
Earth-sun distance (average) 1 . 496 × 10 11 m 1 . 496 × 10 11 m size 12{1 "." "496" times "10" rSup { size 8{"11"} } " m"} {}
Earth mass 5 . 9736 × 10 24 kg 5 . 9736 × 10 24 kg size 12{5 "." "9736" times "10" rSup { size 8{"24"} } `"kg"} {}
average radius 6 . 376 × 10 6 m 6 . 376 × 10 6 m size 12{6 "." "376" times "10" rSup { size 8{6} } `m} {} {}
orbital period 3 . 16 × 10 7 s 3 . 16 × 10 7 s size 12{3 "." "16" times "10" rSup { size 8{7} } " s "} {}
Moon mass 7 . 35 × 10 22 kg 7 . 35 × 10 22 kg size 12{7 "." "35" times "10" rSup { size 8{"22"} } `"kg"} {}
average radius 1 . 74 × 10 6 m 1 . 74 × 10 6 m size 12{1 "." "74" times "10" rSup { size 8{6} } `m} {}
orbital period (average) 2 . 36 × 10 6 s 2 . 36 × 10 6 s size 12{2 "." "36" times "10" rSup { size 8{6} } " s"} {}
Earth-moon distance (average) 3 . 84 × 10 8 m 3 . 84 × 10 8 m size 12{3 "." "84" times "10" rSup { size 8{8} } " m"} {}
Table C3

Solar System Data

Prefix Symbol Value Prefix Symbol Value
tera T 10 12 10 12 size 12{"10" rSup { size 8{"12"} } } {} deci d 10 1 10 1 size 12{"10" rSup { size 8{ - 1} } } {}
giga G 10 9 10 9 size 12{"10" rSup { size 8{9} } } {} centi c 10 2 10 2 size 12{"10" rSup { size 8{ - 2} } } {}
mega M 10 6 10 6 size 12{"10" rSup { size 8{6} } } {} milli m 10 3 10 3 size 12{"10" rSup { size 8{ - 3} } } {}
kilo k 10 3 10 3 size 12{"10" rSup { size 8{3} } } {} micro μ μ size 12{μ} {} 10 6 10 6 size 12{"10" rSup { size 8{ - 6} } } {}
hecto h 10 2 10 2 size 12{"10" rSup { size 8{2} } } {} nano n 10 9 10 9 size 12{"10" rSup { size 8{ - 9} } } {}
deka da 10 1 10 1 size 12{"10" rSup { size 8{1} } } {} pico p 10 12 10 12 size 12{"10" rSup { size 8{ - "12"} } } {}
10 0 ( = 1 ) 10 0 ( = 1 ) size 12{"10" rSup { size 8{0} } \( `=1` \) } {} femto f 10 15 10 15 size 12{"10" rSup { size 8{ - "15"} } } {}
Table C4

Metric Prefixes for Powers of Ten and Their Symbols

Alpha Α Α size 12{Α} {} α α size 12{α} {} Eta Η Η size 12{Η} {} η η size 12{η} {} Nu Ν Ν size 12{Ν} {} ν ν size 12{ν} {} Tau Τ Τ size 12{Τ} {} τ τ size 12{τ} {}
Beta Β Β size 12{Β} {} β β size 12{β} {} Theta Θ Θ size 12{Θ} {} θ θ size 12{θ} {} Xi Ξ Ξ size 12{Ξ} {} ξ ξ size 12{ξ} {} Upsilon Υ Υ size 12{Υ} {} υ υ size 12{υ} {}
Gamma Γ Γ size 12{Γ} {} γ γ size 12{γ} {} Iota Ι Ι size 12{Ι} {} ι ι size 12{ι} {} Omicron Ο Ο size 12{Ο} {} ο ο size 12{ο} {} Phi Φ Φ size 12{Φ} {} ϕ ϕ size 12{ϕ} {}
Delta Δ Δ size 12{Δ} {} δ δ size 12{δ} {} Kappa Κ Κ size 12{Κ} {} κ κ size 12{κ} {} Pi Π Π size 12{Π} {} π π size 12{π} {} Chi Χ Χ size 12{Χ} {} χ χ size 12{χ} {}
Epsilon Ε Ε size 12{Ε} {} ε ε size 12{ε} {} Lambda Λ Λ size 12{Λ} {} λ λ size 12{λ} {} Rho Ρ Ρ size 12{Ρ} {} ρ ρ size 12{ρ} {} Psi Ψ Ψ size 12{Ψ} {} ψ ψ size 12{ψ} {}
Zeta Ζ Ζ size 12{Ζ} {} ζ ζ size 12{ζ} {} Mu Μ Μ size 12{Μ} {} μ μ size 12{μ} {} Sigma Σ Σ size 12{Σ} {} σ σ size 12{σ} {} Omega Ω Ω size 12{ %OMEGA } {} ω ω size 12{ω} {}
Table C5

The Greek Alphabet

Entity Abbreviation Name
Fundamental units Length m meter
Mass kg kilogram
Time s second
Current A ampere
Supplementary unit Angle rad radian
Derived units Force N = kg m / s 2 N = kg m / s 2 size 12{N="kg" cdot {m} slash {s rSup { size 8{2} } } } {} newton
Energy J = kg m 2 / s 2 J = kg m 2 / s 2 size 12{J="kg" cdot {m rSup { size 8{2} } } slash {s rSup { size 8{2} } } } {} joule
Power W = J / s W = J / s size 12{W= {J} slash {s} } {} watt
Pressure Pa = N / m 2 Pa = N / m 2 size 12{"Pa"= {N} slash {m rSup { size 8{2} } } } {} pascal
Frequency Hz = 1 / s Hz = 1 / s size 12{"Hz"= {1} slash {s} } {} hertz
Electronic potential V = J / C V = J / C size 12{V= {J} slash {C} } {} volt
Capacitance F = C / V F = C / V size 12{F= {C} slash {V} } {} farad
Charge C = s A C = s A size 12{C=s cdot A} {} coulomb
Resistance Ω = V / A Ω = V / A size 12{ %OMEGA = {V} slash {A} } {} ohm
Magnetic field T = N / A m T = N / A m size 12{T= {N} slash { left (A cdot m right )} } {} tesla
Nuclear decay rate Bq = 1 / s Bq = 1 / s size 12{"Bq"= {1} slash {s} } {} becquerel
Table C6

SI Units

Length 1 inch ( in . ) = 2 . 54 cm ( exactly ) 1 inch ( in . ) = 2 . 54 cm ( exactly ) size 12{1" inch " \( "in" "." \) =2 "." "54"" cm " \( "exactly" \) } {}
1 foot ( ft ) = 0 . 3048 m 1 foot ( ft ) = 0 . 3048 m size 12{1" foot " \( "ft" \) =0 "." "3048"" m"} {}
1 mile ( mi ) = 1 . 609 km 1 mile ( mi ) = 1 . 609 km size 12{1" mile " \( "mi" \) =1 "." "609"" km"} {}
Force 1 pound ( lb ) = 4 . 448 N 1 pound ( lb ) = 4 . 448 N size 12{1" pound " \( "lb" \) =4 "." "448"" N"} {}
Energy 1 British thermal unit ( Btu ) = 1 . 055 × 10 3 J 1 British thermal unit ( Btu ) = 1 . 055 × 10 3 J size 12{1" British thermal unit " \( "Btu" \) =1 "." "055" times "10" rSup { size 8{3} } " J"} {}
Power 1 horsepower ( hp ) = 746 W 1 horsepower ( hp ) = 746 W size 12{1" horsepower " \( "hp" \) ="746"" W"} {}
Pressure 1 lb / in 2 = 6 . 895 × 10 3 Pa 1 lb / in 2 = 6 . 895 × 10 3 Pa size 12{1 {"lb"} slash {"in" rSup { size 8{2} } } =6 "." "895" times "10" rSup { size 8{3} } " Pa"} {}
Table C7

Selected British Units

Length 1 light year ( ly ) = 9 . 46 × 10 15 m 1 light year ( ly ) = 9 . 46 × 10 15 m size 12{1`" light"`" year"` \( "ly" \) ` =9 "." "46" times "10" rSup { size 8{"15"} } " m"} {}
1 astronomical unit ( au ) = 1 . 50 × 10 11 m 1 astronomical unit ( au ) = 1 . 50 × 10 11 m size 12{1`" astronomical"`" unit"` \( "au" \) ` =1 "." "50" times "10" rSup { size 8{"11"} } " m"} {}
1 nautical mile = 1 . 852 km 1 nautical mile = 1 . 852 km size 12{1`" nautical"`" mile"` =1 "." "852"`" km"} {}
1 angstrom ( Å ) = 10 10 m 1 angstrom ( Å ) = 10 10 m size 12{1`" angstrom"` \( Å \) ` ="10" rSup { size 8{ - "10"} } " m"} {}
Area 1 acre ( ac ) = 4 . 05 × 10 3 m 2 1 acre ( ac ) = 4 . 05 × 10 3 m 2 size 12{1`" acre"` \( "ac" \) ` =4 "." "05" times "10" rSup { size 8{3} } " m" rSup { size 8{2} } } {}
1 square foot ( ft 2 ) = 9 . 29 × 10 2 m 2 1 square foot ( ft 2 ) = 9 . 29 × 10 2 m 2 size 12{1`"square"`"foot"` \( "ft" rSup { size 8{2} } \) ` =9 "." "29" times "10" rSup { size 8{ - 2} } " m" rSup { size 8{2} } } {}
1 barn ( b ) = 10 28 m 2 1 barn ( b ) = 10 28 m 2 size 12{1`" barn"` \( b \) ` ="10" rSup { size 8{ - "28"} } " m" rSup { size 8{2} } } {}
Volume 1 liter ( L ) = 10 3 m 3 1 liter ( L ) = 10 3 m 3 size 12{1`" liter"` \( L \) ` ="10" rSup { size 8{ - 3} } " m" rSup { size 8{3} } } {}
1 U.S. gallon ( gal ) = 3 . 785 × 10 3 m 3 1 U.S. gallon ( gal ) = 3 . 785 × 10 3 m 3 size 12{1`" U" "." S "." `" gallon"` \( "gal" \) ` =3 "." "785" times "10" rSup { size 8{ - 3} } " m" rSup { size 8{3} } } {}
Mass 1 solar mass = 1 . 99 × 10 30 kg 1 solar mass = 1 . 99 × 10 30 kg size 12{1`" solar"`" mass"` =1 "." "99" times "10" rSup { size 8{"30"} } " kg"} {}
1 metric ton = 10 3 kg 1 metric ton = 10 3 kg size 12{1`" metric"`" ton"` ="10" rSup { size 8{3} } " kg"} {}
1 atomic mass unit ( u ) = 1 . 6605 × 10 27 kg 1 atomic mass unit ( u ) = 1 . 6605 × 10 27 kg size 12{1`" atomic"`" mass"`" unit"`` \( u \) ` =1 "." "6605" times "10" rSup { size 8{ - "27"} } " kg"} {}
Time 1 year ( y ) = 3 . 16 × 10 7 s 1 year ( y ) = 3 . 16 × 10 7 s size 12{1`" year"` \( y \) ` =3 "." "16" times "10" rSup { size 8{7} } " s"} {}
1 day ( d ) = 86 , 400 s 1 day ( d ) = 86 , 400 s size 12{1`" day"` \( d \) ` ="86","400"`" s"} {}
Speed 1 mile per hour ( mph ) = 1 . 609 km / h 1 mile per hour ( mph ) = 1 . 609 km / h size 12{1`" mile"`"per"`"hour"` \( "mph" \) `=1 "." "609"` {"km"} slash {h} } {}
1 nautical mile per hour ( naut ) = 1 . 852 km / h 1 nautical mile per hour ( naut ) = 1 . 852 km / h size 12{1`" nautical"`"mile"`"per"`"hour"` \( "naut" \) `=1 "." "852"` {"km"} slash {h} } {}
Angle 1 degree ( ° ) = 1 . 745 × 10 2 rad 1 degree ( ° ) = 1 . 745 × 10 2 rad size 12{1`" degree"` \( ° \) ` =1 "." "745" times "10" rSup { size 8{ - 2} } " rad"} {}
1 minute of arc ( ' ) = 1 / 60 degree 1 minute of arc ( ' ) = 1 / 60 degree size 12{1`" minute"`"of"`"arc"` { { \( }} sup { ' } \) `= {1} slash {"60"} `" degree"} {}
1 second of arc ( '' ) = 1 / 60 minute of arc 1 second of arc ( '' ) = 1 / 60 minute of arc size 12{1`" second"`"of"`"arc"` { { \( }} sup { '' } \) `= {1} slash {"60"`} " minute of arc"} {}
1 grad = 1 . 571 × 10 2 rad 1 grad = 1 . 571 × 10 2 rad size 12{1`" grad"` =1 "." "571" times "10" rSup { size 8{ - 2} } " rad"} {}
Energy 1 kiloton TNT ( kT ) = 4 . 2 × 10 12 J 1 kiloton TNT ( kT ) = 4 . 2 × 10 12 J size 12{1`" kiloton"`" TNT"` \( "kT" \) ` =4 "." 2 times "10" rSup { size 8{"12"} } " J"} {}
1 kilowatt hour ( kW h ) = 3 . 60 × 10 6 J 1 kilowatt hour ( kW h ) = 3 . 60 × 10 6 J size 12{1`" kilowatt"`" hour"` \( "kW" cdot h \) ` =3 "." "60" times "10" rSup { size 8{6} } " J"} {}
1 food calorie ( kcal ) = 4186 J 1 food calorie ( kcal ) = 4186 J size 12{1`" food"`"calorie"` \( "kcal" \) `="4186"`" J"} {}
1 calorie ( cal ) = 4 . 186 J 1 calorie ( cal ) = 4 . 186 J size 12{1`" calorie"` \( "cal" \) `=4 "." "186"`" J"} {}
1 electron volt ( eV ) = 1 . 60 × 10 19 J 1 electron volt ( eV ) = 1 . 60 × 10 19 J size 12{1`" electron"`" volt"` \( "eV" \) ` =1 "." "60" times "10" rSup { size 8{ - "19"} } " J"} {}
Pressure 1 atmosphere ( atm ) = 1 . 013 × 10 5 Pa 1 atmosphere ( atm ) = 1 . 013 × 10 5 Pa size 12{1`" atmosphere"` \( "atm" \) ` =1 "." "013" times "10" rSup { size 8{5} } " Pa"} {}
1 millimeter of mercury ( mm Hg ) = 133 . 3 Pa 1 millimeter of mercury ( mm Hg ) = 133 . 3 Pa size 12{1`" millimeter"`"of"`"mercury"` \( "mm"`"Hg" \) `="133" "." 3`" Pa"} {}
1 torricelli ( torr ) = 1 mm Hg = 133 . 3 Pa 1 torricelli ( torr ) = 1 mm Hg = 133 . 3 Pa size 12{1`" torricelli"` \( "torr" \) `=1`" mm"``"Hg "="133" "." 3`" Pa"} {}
Nuclear decay rate 1 curie ( Ci ) = 3 . 70 × 10 10 Bq 1 curie ( Ci ) = 3 . 70 × 10 10 Bq size 12{1`" curie"` \( "Ci" \) ` =3 "." "70" times "10" rSup { size 8{"10"} } " Bq"} {}
Table C8

Other Units

Circumference of a circle with radius rr size 12{r} {} or diameter dd size 12{d} {} C = 2 πr = πd C = 2 πr = πd size 12{C=2πr=πd} {}
Area of a circle with radius rr size 12{r} {} or diameter dd size 12{d} {} A = πr 2 = πd 2 / 4 A = πr 2 = πd 2 / 4 size 12{A=πr rSup { size 8{2} } = {πd rSup { size 8{2} } } slash {4} } {}
Area of a sphere with radius rr size 12{r} {} A = 4 πr 2 A = 4 πr 2 size 12{A=4πr rSup { size 8{2} } } {}
Volume of a sphere with radius rr size 12{r} {} V = 4 / 3 πr 3 V = 4 / 3 πr 3 size 12{V= left ( {4} slash {3} right ) left (πr rSup { size 8{3} } right )} {}
Table C9

Useful Formulae

Footnotes

  • 1 Stated values are according to the National Institute of Standards and Technology Reference on Constants, Units, and Uncertainty, www.physics.nist.gov/cuu (accessed May 18, 2012). Values in parentheses are the uncertainties in the last digits. Numbers without uncertainties are exact as defined.
  • 2 Stated values are according to the National Institute of Standards and Technology Reference on Constants, Units, and Uncertainty, www.physics.nist.gov/cuu (accessed May 18, 2012). Values in parentheses are the uncertainties in the last digits. Numbers without uncertainties are exact as defined.