Each time the weaver moved the sley to beat-up the weft, a rachet and pawl mechanism advanced the cloth roller.
[1] In 1802 William Ratcliffe of Stockport patented a Dandy loom with a cast-iron frame.
The dandy loom increased the productivity of a hand-loom weaver by 50%.
It is difficult: the output of power looms was certainly greater than that of the handlooms, but the handloom weavers produced higher quality cloths with greater profit margins.
The weaving trade was only partially mechanised before about 1830, and that even so late as 1850, handloom weavers made up a sizeable minority of the total workforce.