What the function of the V-shaped mirror or the rotating disc in double beam spectrophotometer.?

In a double beam spectrophotometer, the V-shaped mirror or rotating disc serves to split the light beam into two paths: one directed towards the sample and the other towards a reference. This configuration allows for simultaneous measurement of the sample and reference, enabling accurate comparisons and compensating for any fluctuations in light intensity. By continuously alternating between the two beams, the device enhances sensitivity and precision in absorbance measurements.