technical reasons, it cannot be used during the 4-hour charging period. What is a dioptre? A dioptre (dpt) is the unit of measurement of the optical power of a lens. In the case of spectacle lenses, negative [...] dioptre is equal to the reciprocal value of the focal length of a lens measured in metres: a power of +5 dpt therefore has a reciprocal length of 1/5 metres or 20 centimetres. What is long-sightedness? In the [...] sufficient for a person to be able to orientate themselves outdoors. However, a visual acuity of 0.8 is required for reading travel timetables. Other minimum values include: 0.4 for watching television
