Standardized ETDRS portable test, Chart 1, Chart 2, Chart R ETDRS Charts, Excellent Correlation with Classic ETDRS Lane Charts (see ref. 4). Take from Room to Room, Office to Office. Eliminates the Dedicated Lane. Optional Charts available for Potential Vision Testing. Voltmeter for Bright Adjustment and Charge Status, Rechargeable Battery.  Validated at Wills Eye Hospital, See Reference #4.  Includes one Chart for Potential Vision Testing (Retinal Acuity). (as of 2/1/2020)