Ludwig Oechslin in an interview with Sam Kessler at Oracle Time:

To be a true watchmaker means that you make the parts of the watches and can calculate how to do it. You have both the mathematical skill to be able to design and understand the concept, and manual feeling for making pieces. Most in the watch industry are not watchmakers; an assembler is not a watchmaker. A watch designer, without the feel for the materials and what you can do with them, is not a good watch designer.