Simplify the following text for a Grade 4 native English-speaking person.
Original: His small , drum-shaped Taschenuhr , a portable watch which he built during his asylum from 1504 to 1508 , could run for forty hours before it needed rewinding .
Simplified: Around 1504 to 1508 Henlein did make a a watch ; a small , drum-shaped Taschenuhr . It could run for forty hours before it needed rewinding .