Functions: (1) Standardized ETDRS portable test, (2) Potential Vision test. Excellent correlation with standard ETDRS Lane Charts (see ref. 4). Take from Room to Room, Office to Office. Eliminates the dedicated ETDRS lane. The voltmeter allows brightness adjustment and battery status, Rechargeable battery. Validated at Wills Eye Hospital, See Reference #4. Includes Chart 1 revised, Chart 2 revised, Chart R for ETDRS testing & one Chart for Potential Vision Testing (Retinal Acuity). Consider 10 Year Extended Warranty.