A new, accurate method for fast and precise optical alignment of crystals in a diamond anvil cell (DAC) on a diffractometer has been developed. It enables highly accurate crystal alignment within instruments with a Boehler-Almax DAC design, achieving precision better than 0.02 mm easily. Other advantages of this method are simplicity, speed and instant visual feedback when aligning the crystal. This method employs Snell's law, which relates the angles of incidence and refraction of light passing through different media to estimate the crystal position within the DAC by measuring the apparent transverse dis-placement of the crystal image at various viewing angles after rotating the DAC by 180°. This information allows for fine-tuning of the crystal alignment within the DAC, ensuring optimal conditions for high-pressure diffraction experiments.