During a retinoscopy, these bars are used, with the different powers. The bars contain glass powers in grades of 0,5 dpt up to 10 dpt. From 10 dpt to 20 dpt the grades are 1,0 dpt. Contained are 2 bars – one with minus and one with plus powers. The slider, which sits on an extra bar, makes your procedure easier and more precise during the retinoscopy.