If you're a designer or architect, this sketching app could make you more efficient. Formerly called Archipad, the Archisketch app from Urban Design is aware of scale (unlike other design apps).
On Archisketch you can pre-determine what the scale of your image is on your in-app drawing sheet. The sketching app will then make sure your completed drawing is scaled to real-world proportions -- even including the thickness of the lines. This is just one great feature of the latest version of the app. Other aspects architects, interior and product designers will appreciate include freehand drawing tools and layer rotations.
The design app has a tiered price, so it's free for small projects but increasingly costly as the work gets more complex.