The inexpensive basic model with all the important basic functions.? Dioptre wheel with 29 corrective lenses Plus 1-10, 12, 15, 20, 40 Minus 1-10, 15, 20, 25, 30, 35? Easy-to-operate aperture hand-wheel with semi-circle, Small/medium/large circle fixation star, slit and red-free filter with contrast-enhancing effect.? Includes filter wheel engageable for all apertures with symbol display, red-free filter.? Optimized high-performance optics with aspherical condenser lens.? Parallel beam path.? Dust-proof.? Large selection of power sources: handy and stable handles, practical chargers and well-conceived diagnostic stations.