a	Adimensional function
A 0	Cross section area at the inlet
A 1	Cross section area at the outlet
A c	Cross section area at the throat
b	Adimensional function
C f	Local skin friction coefficient
d, D	Nozzle exit diameter
f	Friction coefficient; focal length
F 0	Force exerted by the gas on the cutting front due to static pressure
F n	Normal component of the dynamic force exerted by the gas on the cutting front
F t	Tangential component of the dynamic force exerted by the gas on the cutting front
M	Mach number
M 0	Mach number at the inlet
M 1	Mach number at the outlet
M c	Mach number at the throat
p	Pressure of the assist gas
p 0	Reference pressure; stagnation pressure
p a	Ambient pressure
p b	Background pressure
p e	Pressure just at the exit of the nozzle
p g	Reduced pressure
P	Laser power
R a	Average roughness
Reg	Reynolds number of the assist gas
t m	Melt film thickness
T	Temperature
U g	Velocity of the assist gas
U m	Velocity of the molten material
v c	Cutting speed
V c	Velocity of the assist gas at the throat of the de Laval nozzle
w	Kerf width
x	Distance along the centerline of the jet; distance along the cutting front or cutting edge
x M	Position of the Mach disk with regard to the nozzle exit
Z	Stand-off
γ	Heat capacity ratio (γ = cp/cv)
ρc	Density of the assist gas at the throat of the de Laval nozzle
ρg	Density of the assist gas
ρm	Density of the molten material
σm	Surface tension of the molten material
τ	Shear stress acting on the cutting front due to the assist gas
φ	Inclination of the cutting front
µg	Dynamic viscosity of the assist gas