I like a good set of reference lines on all my forms. These are usually supplied by gluing the paper form patterns to the MDF and leaving them there. The patterns have the reference lines so everything is good. But I'm making the Nymph and it is symmetrical so being lazy I can make two sets of forms at the same time by stacking up two pieces of MDF and cutting them both at once. But, this means the paper pattern is only on one of the two copies.
To get around this I start by putting the nails in a useful spot, in this case at the intersection of the reference lines. Then I make a little cut with the bandsaw where ever the reference line hit the edge of the form. This way I have a ready made set of points to connect with a ruler and a pencil.