https://developer.garmin.com/connect-iq/api-docs/Toybox/Graphics/AffineTransform.html
The doc at the above link has several references to the "cross product" of two matrices (or a matrix and a vector), but I think a more appropriate term would be "matrix product". Referring to matrix multiplication as a "cross product" is a bit misleading / confusing, especially if you took linear algebra or vector calculus in college.
