YouTube video by Marcell Mrsan explaining his grading ruler
Notes
- demo: children’s lasts
- US 5 versus US 4
- difference 8%
- measures bottom length
- suggests using cm
- 12.5 cm versus 13.4 cm, round up
- example: grading bottom paper from 4 to 5
- traces outline
- Theory
- line of given length from A to B
- want to make e.g. 10% longer, to C
- perpendicular line
- make right triangle of A, B, and C
- fixed ratio of hypotenuse
- ruler has calculations via lines
- finding center line
- not right in the middle
- picks pivot point way off to bottom left
- draws straight rays out from that point
- projects new points a given percentage longer
- then connects new points around old tracing
- checks new bottom paper against larger last