Digital Biometric Ruler with Built-In Calibration Cylinder is available with multiple screen display for tabled, summarized and compared calculations. National Industrial Company offers Digital Biometric Ruler with Built-In Calibration Cylinder. National Industrial Company supplies wide ranges of auto chart projector refract meter, auto ref/keratometer, automated perimeter, binocular loupes, diamond knives, green laser, handles, hand held slit lamp, head lights, indirect ophthalmoscopes, lenses etc. Digital Biometric Ruler with Built-In Calibration Cylinder is available under the model number- A-5500, comes with automatic with built-in calibration cylinder.