import type { MeasurementXYVariables } from 'cheminfo-types';
/**
 * Callback that adds absorbance (a) and transmittance (t) variables to the spectrum.
 * If the y variable is absorbance, transmittance is computed and vice versa.
 * @param variables - Spectrum variables with at least x and y defined.
 * @returns The modified variables with a and t added.
 */
export declare function spectrumCallback(variables: MeasurementXYVariables): MeasurementXYVariables;
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