Toyota knit-tracer K20 assists machine-knitters with decreases and increases based on their calculated gauge. Refer to a manual (available online for free) for more details.

According to some sources, K20 knit tracers fit the following Toyota knitting machines: KS510, KS747, and some others.

Other charting devices from Toyota are K31, K32, K33 and K33A.

Stay tuned as I am figuring out more.