Simple microscope is used for watch repairs.

Explanation

i. A magnification of about 20 times is obtained by simple microscope.
ii. When an object is placed within the focal length of convex lens, one gets a magnified and erect image of the object.
iii. Thus, the watch repairer can see the minute parts of the watch more clearly with the help of simple microscope than the naked eye, without any strain on the eye. Hence, simple microscope is used for watch repairs.