Code 3685 applies to employers engaged in manufacturing professional or scientific instruments designed for use in research or work that is strictly of a professional or scientific nature.  The products that are contemplated under this classification are products such as air pressure gauges, steam gauges, speedometers or taximeters (fare meters), thermometers and similar products.  Depending upon the product being manufactured the operations may vary which could include machining, heat treating, and stamping.  The component parts are usually manufactured by other concerns.  Employers will perform a substantial portion of hand assembly, testing and packaging.