I just watched the demo just uploaded to YouTube titled Shapr3d Holes. Fairly basic and uses metric.
As I watched the video I realized that the only way I could relate dynamically to lengths in mm was to translate back through English/Imperial as I had memorized 1” = 2.54 cm and I can relate to an inch and that a meter is about 10% longer than a yard. A mm to me is just something small although I now remember that 8mm is about a 30 caliber bullet (0.30”). Furthermore I relate that 1” is about the length of the tip of my thumb to its first joint, 1 foot is about the length of my foot and 1 yard is about the length of my arm.
So, I wondered if metrically raised children/people have similar bio comparisons? Or any type of comparisons to everyday common objects? Inquiring minds, you know?