5 different apertures. 19 kinds of adjustable corrective lenses; range of lenses: -20D-+20D. The clip with integrated on/ off switch for simple use. Powered by 2xAA batteries (not included), easy to install and replace batteries. Compact size and design for easy storage and convenient transport. Elaborate design and reliable quality. A classic instrument for physician. Illumination: Direct Illumination Luminance: 14 Lumen Bulb: 106 2.5V, 0.5A; 206 3.0V, 0.08A Operation: Temperature 10-35, Humidity 30%-70%, Air Pressure 700hPa-1060hPa Storage & Transport: -20-70, Humidity 10%-90% (without condensation), Air Pressure 500hPa-1060hPa Colour:As Shown Material:ABS+Metal Package Contents: 1 x Eye Checker Only the above package content, other products are not included. Note: Light reflection and different displays may cause the color of the item in the picture a little different from the real thing. The measurement allowed error is +/- 1-3cm.