Original: Although many sources erroneously credit Henlein with the invention of the mainspring , descriptions and two surviving examples show that spring-driven clocks existed by the early 15th century/O. , p. 121 , p. 440 , p. 305 , p.126-127 , p. 121
Simplified: Although many say that Henlein invented the mainspring , there are descriptions and two surviving examples show that spring driven clocks had already been made by the early 1400s .