A watch movement is defined in Chapter 91 notes by its size and construction — generally a movement with a greatest linear dimension not exceeding 50 mm, designed with the precision and jeweling characteristics of a personal timepiece movement. A clock movement is larger and built to different tolerances. The physical dimensions and technical specifications of the movement itself, not the clock's external size, govern the classification.

It depends on whether the quartz movement meets the Chapter 91 definition of a watch movement. Many small quartz clock movements used in decorative clocks are purpose-built clock movements that do not meet the watch-movement size and construction criteria, placing the article under 9105. If the movement is genuinely watch-grade (e.g., sourced from a watch movement manufacturer and meeting the dimensional threshold), 9103 would apply.