In a self-referencing instrument for measuring electromagnetic radiation, a mounting member to which a sample can be coupled moves the sample such that, in a first position, the electromagnetic radiation impinges on the sample, and, in a second position, the electromagnetic radiation does not impinge on the sample. A detection unit receives the electromagnetic radiation from the sample and generates a sample signal when the sample is in the first position, and the detection unit receives the electromagnetic radiation from the source and generates a reference signal when the sample is in the second position. A processor coupled to the detection unit processes the reference signal and the sample signal. This results in a continuous, accurate reference measurement, and permits the instrument to efficiently compensate for error, while offering accurate measurements.