Как называют отрезок, длина которого принята за единицу измерения?

Russian gymnast Aliya Mustafina won gold at the Olympic games in London. Her pride of the whole country. Aliya,from childhood engaged in gymnastics, stretching her,her movement gives her an advantage. She quickly flies with bars, smoothly jumping on a log. In my 17 years it has achieved a lot in. Российская гимнастка алия мустафина

Maria was born April 19, 1987 in Nyagan, a town in western Siberia, where her parents, Yuri and Yelena, had fled from Belarus a year earlier to avoid radiation from Chernobyl.