--- /dev/null
+bsplinecurve b1 3 5 0 4 1 1 2 1 3 1 4 4 0 0 0 0.8 1 0.5 0 0.6 2 1 0 0.5 2 2 0 1 3 1.5 0 1 4 1.5 0 1 5 2 0 1
+cvalue b1 2.0 x y z dx dy dz
+set delta 0.01
+set yvalue [dval y]
+set zvalue [dval z]
+repeat 100 {
+ cmovetangent b1 2.0 x $yvalue $zvalue dx dy dz 1
+ set yvalue [expr $yvalue + $delta ]
+ set zvalue [expr $zvalue + $delta ]
+ repaint }
+renamevar b1 result
+set length 7.3508406963557418
+