A	auxiliary parameters [m3] or [kPa]
a	width or minor axis of ellipse [m]
B	auxiliary parameters [m5/kN] or [kPa]
b	length or major axis of ellipse [m]
c	auxiliary parameters [kPa]
D	flexural rigidity (of glass pane) [kNm]
d	thickness (of glass pane) [m] or [mm]
E	Young’s modulus [kPa] or [GPa]
f	diameter of circular IGU [m]
i	consecutive natural number
k	dimensionless coefficient regarding stress [-]
M	molecular weight [g/mol]
p	pressure [kPa]
q	resultant load (of glass pane) or outside load [kN/m2]
R	radius of circular IGU [m]
Ru	universal gas constant [J/(K·mol)]
r	coordinate in the polar system
T	temperature (of gas in the gap) [K] or [°C]
U	thermal transmittance [W/(m2·K)]
v	volume (of the gap) [m3]
w	deflection [m] or [mm]
w(r)	function of deflection (circular IGU), [m]
w(x,y)	function of deflection [m]
x-y	coordinate system
Greek Letters
α	proportionality factor, [m5/kN]
α′	dimensionless coefficient [-]
γ	specific gravity of glass [kN/m3]
μ	Poisson’s ratio [-]
π	number “pi”
∑Δv	change in gap volume [m3]
σ	stress [MPa]
φ	slope to horizontal [deg]
Subscripts and Markings
0	initial gas parameters
1, 2 …	specific gas-filled gap
1-2, 2-3 …	glass pane (between gaps)
a	atmospheric
air	regarding air
ex	exterior glass pane
g	index that relates to glazing
in	interior glass pane
n	number of gas gaps
op	operating gas parameters
r	regarding circular IGU
v	index that relates to volume
w	index that relates to deflection
z	outside
γ	index that relates to specific gravity