An analytical and experimental methodology for evaluating functional characteristics of the single-thread chainstitch formation process (type 101) is proposed. The evaluation is based on degree of correspondence between the required and actual thread take-up, which reflects the machine’s efficiency and the quality of stitch formation. A measuring system and an experimental procedure were developed to record thread takeup under different material thicknesses and stitch lengths. The obtained dependencies were approximated by sixth-egree polynomials with high accuracy (R² > 0.99), which made it possible to construct mathematical models of the thread takeup process. For GK-9 type machines, excessive thread take-up (20–64% above the required value) was set up, causing uneven thread tension and reduced stitch stability. The proposed methodology ensures quantitative evaluation, prediction, and regulation of thread take-up process, which improves functional efficiency of sewing machines and supports development of adaptive thread take-up control systems.