§ 1066.705 - Symbols, abbreviations, acronyms, and units of measure.

The procedures in this part generally follow either the International System of Units (SI) or the United States customary units, as detailed in NIST Special Publication 811, which we incorporate by reference in §1066.710. See 40 CFR 1065.20 for specific provisions related to these conventions. This section summarizes the way we use symbols, units of measure, and other abbreviations.

(a) Symbols for quantities. This part uses the following symbols and units of measure for various quantities:

Symbol	Quantity	Unit	Unit symbol	Unit in terms of SI base units
a	acceleration	feet per second squared or meters per second squared	ft/s2 or m/s2	m·s−2
d	diameter	meters	m	m
F	force	pound force or newton	lbf or N	kg·s−2
f	frequency	hertz	Hz	s−1
I	inertia	pound mass or kilogram	lbm or kg	kg
i	indexing variable
M	mass	pound mass or kilogram	lbm or kg	kg
N	total number in series
n	total number of pulses in a series
R	dynamometer roll revolutions	revolutions per minute	rpm	2·π·60−1·  m·m−1·s−1
RL	road-load coefficient	horsepower or kilowatt	hp or kW	103·m2·kg·s−3
S	speed	miles per hour or meters per second	mph or m/s	m·s−1
T	Celsius temperature	degree Celsius	°C	K-273.15
T	torque (moment of force)	newton meter	N·m	m2·kg·s−2
t	time	second	s	s
Δt	time interval, period, 1/frequency	second	s	s
y	generic variable

(b) Symbols for chemical species. This part uses the following symbols for chemical species and exhaust constituents:

Symbol	Species
CH4	methane
CO	carbon monoxide
CO2	carbon dioxide
NMHC	nonmethane hydrocarbon
NMHCE	nonmethane hydrocarbon equivalent
NO	nitric oxide
NO2	nitrogen dioxide
NOX	oxides of nitrogen
N2O	nitrous oxide
O2	molecular oxygen
PM	particulate mass
THC	total hydrocarbon
THCE	total hydrocarbon equivalent

(c) Superscripts. This part uses the following superscripts to define a quantity:

Superscript	Quantity
overbar (such as) y	arithmetic mean

(d) Subscripts. This part uses the following subscripts to define a quantity:

Subscript	Quantity
int	speed interval
abs	absolute quantity
act	actual or measured condition
actint	actual or measured condition over the speed interval
atmos	atmospheric
b	base
c	coastdown
e	effective
error	error
exp	expected quantity
i	an individual of a series
final	final
init	initial quantity, typically before an emission test
max	the maximum (i.e., peak) value expected at the standard over a test interval; not the maximum of an instrument range
meas	measured quantity
ref	reference quantity
rev	revolution
roll	dynamometer roll
s	settling
sat	saturated condition
si	speed interval
span	span quantity
test	test quantity
uncor	uncorrected quantity
zero	zero quantity

(e) Other acronyms and abbreviations. This part uses the following additional abbreviations and acronyms:

CFR	Code of Federal Regulations
EPA	Environmental Protection Agency
FID	flame-ionization detector
GVWR	gross vehicle weight rating
NIST	National Institute for Standards and Technology
RESS	rechargeable energy storage system
SAE	Society of Automotive Engineers
U.S.C.	United States Code