This is about enlarging curves. I give Daren drawings that must be enlarged exactly as I drew them. This is how he does it.
Daren draws a grid on tracing paper, laying it over the design. This correlates exactly with a second, full-size grid. Where lines cross the grid, Daren makes a small mark. This is transferred to the second grid, at the same exact point.
On the larger grid, those marks are then joined up by bending a long steel rule so the edge of the rule hits the crosses. Another maker then draws a clean line guided by the curved steel. Easy when you know how…