Originally Posted by family wagon
Keep in mind when tracing with a spacer like the block of wood that if you're copying anything but a straight line, then you're actually going to get a reduced copy. Envision using the spacer block to trace inside a circle -- the copied circle, while being a perfect match to the original shape, will be smaller by the thickness of the block plus half the thickness of the pencil/pen/marker.
I like to use the block method until my template is "pretty close" and then remove the block and use the pencil alone, perhaps even held so that the tapered/sharpened tip instead of the whole body runs on the tracing surface. The nearer the line is drawn to the surface you're tracing, the less the shrinking effect will be.
By taping the wooden block to the pencil in a slightly different way you can avoid the shrinking effect.
Take the pencil and a block of wood as thick as the pencil and tape it to the pencil so that it is sticking out width-wise. Now bring the pencil+block up to the bottom of the curve and keep the block horizontal. Trace the curve while always keeping the block horizontal and you will end up with a near perfect curve.