You can find which Adafruit boards have the re library here. Please ensure all dependencies are available on the CircuitPython filesystem. This is easily achieved by ...
Where: A = absorbance, epsilon = extinction coefficient (M^-1 cm^-1), c = concentration (M), l = path length (cm) To convert ppm to molarity: M = ppm / (molecular_weight_g/mol) / 1000 UV-Visible ...