The refers to a specific version of Stoll’s pattern preparation software. Versions around the 3.1x series were pivotal in bridging the gap between basic pattern design and fully automated machine programming. This software acts as the translator between a designer’s creative vision (a CAD drawing or a scanned sketch) and the machine language (a stitch program) that a Stoll flat knitting machine understands.
While you are looking for a "free download," most official documentation and software for these industrial machines are proprietary. However, you can often find the documentation and related technical papers through the following resources: M1 Stoll 3.15 Free Download
