When you start a new part model and create the first sketch for the first feature you will draw a shape the "looks" to be about the size you want but most times it will be way bigger then what you want. For example you want to start with a rectangle that is 10 x 20 (inches or mm) but you end up with a rectangle that is 110 x 225. The only solution to this that I'm aware of is to zoom way in (or maybe way out if you want to start really big) before you start your sketch but this is very subjective and not precise. It would be nice if there was some way to define an initial scale or zoom factor that would allow you to start sketching at roughly the correct size of your average part.
