Catchbook turns hand drawn strokes into curves that you can edit.
These 4 videos take you through the basics of how to create and edit curves in Catchbook.
When you draw "ink" on the screen with your finger or stylus, Catchbook works out what curves best fit the path you have drawn and connects them all up. You can then edit these curves to get exactly the right shape. Hint: turn on the recognition button (the trianglular one) on the main toolbar to turn your ink into curves as you draw.
More curve editing. Hint - Double tap to change circles into ellipses and lines into arcs: