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All of the source code to this project is available under licenses which are both free and open source.
Most of it is available under GNU GPL and MIT License.

The remainder of the software which is not under the GNU GPL is available under one of a variety of other licenses. Those that require reproduction of the license text in the distribution are given below.
(Note: Your copy of this product may not contain code covered by one or more of the licenses listed here, depending on the exact product and version you choose.)

Legend

λ

Wavelength [nm]

B^o

Beam (measuring) angle [^o]
180 ^o: Transmitted light measurement (Absorbance)
90 ^o: Nephelometric turbidity (scattered light) measurement

I₀

Intensity of incident light [lux]

I_T

Intensity of transmitted light [lux]

T = I_T / I₀

Transmission
Energy passing through
Range: 1.0 - 0.0

A = 1 - T

Absorption
Energy lost

E_λ = - log ( T ) = ε_λ * c * d

Absorbance
Attenuation
Lambert-Beer law
Optimum range: 0.1 – 1.0

SAC_λ = E_λ / d * 100

Spectral Absorption Coefficient [m^-1]

c = E_λ / ( ε_λ * d ) = E_λ * F

Concentration of absorbing substance in the liquid [mol/l]

F = 1 / ( ε_λ * d )

Factor
Test specific

ε_λ

Molar decadic extinction coefficient [l/mol/cm]

d

Thickness of the solution layer [cm]

Turbidity

Opacity, clouding, haze

FNU

Formazine Nephelometric Unit

NTU

Nephelometric Turbidity Unit

FAU

Formazine Attenuation Unit

Measurement methods

Photometry

Absorbance measurement (transmitted light or absorption measurement)
Recommended measuring range: 40–4000 FAU (DIN EN ISO 7027)
Light source and detector are located on the same axis (180° angle).
The reduced light intensity which remains after passing through the sample is measured

Nephelometry

Scattered light measurement
Recommended measuring range: 0–40 FNU (DIN EN ISO 7027)
Light source and detector are oriented at an angle of 90° relative to each other