Nice but too slow
The app looks great, but it is a bit slow. Draw a circle mildly fast and you will get an angular shape (iPad 1). In my opinion this is a no go for any drawing/sketching app. A larger sponge would be nice and a pressure slider for the chalk might be a nice thing to have. Fancy idea for further development: wet sponge with a drying chalkboard effect and wet chalk look.
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Bord, v1.1