12dbsplinecurve b1 3 5 0 4 1 1 2 1 3 1 4 4  0 0 1  1 0.5 0.8   2 1 1  2 2 0.7  3 1.5 0.6  4 1.5 1   5 2 1
22dcvalue b1 2.0 x y  dx dy
3set delta 0.01
4point p1 x y
5set dyvalue [dval dy]
6repeat 100 {
7    cmovetangent b1 2.0  x y dx $dyvalue 1
8    set dyvalue [expr $dyvalue + $delta ]
9    repaint
10}
11copy b1 result
12checklength result -l 6.6492776719511806