This chapter outlines the prerequisites for solving the problem of increasing the efficiency of mechanical assembly production on the basis of creating a new method and system of technological preparation for small-scale production in instrumentation, which considers the dominant influence of assembly processes on the time and cost of manufacturing devices. A new structure and sequence of technological preparation of instrumentation production with a formalized relationship between machining and assembly production is proposed. A new model of an assembly product in instrumentation has been developed, which considers the labor intensity and specifics of assembly, adjustment, and control and measurement work and methods of computer-aided design of technological processes for assembling instruments. A functional model of the product structure formation based on the labor intensity of the assembly units manufacturing is also proposed, which allows to form a reasonable plan for the parts manufacturing and a mathematical model of the assembly sequence, which allows to build the assembly sequence considering organizational and technical factors. Thus, the aim of this work is to increase the efficiency of mechanical assembly production by creating a new method and system of technological preparation for small-scale production in instrumentation, considering the dominant influence of assembly processes on the time of manufacturing of devices.