In the case of the Corvette, first I cut a paper template of the shape of the bow. I then marked it with the water line and scale 1 foot increments, above and below. I used this template to create a word Document with the line spacing the same as the depth increments and the indentation of the numerals matching the shape of the template. I went through a few pieces of paper, test printing them and matching them up to the template. When I had the bow numerals as I wanted them the aft numbers, being vertical. were easy to create by simply using the Tab on each line.
Once I had a word document with everything arranged to give me a couple of decals of each type I converted it to a .pdf, which is the format the decal printing service requires. I created the original in Word as it is so much more flexible to work with and, as you resize things it automatically adjusts things to give sharp edges. If you use a photo editing program and you resize you can end up with poorly defined edges. Also rearranging things to fill the space of say half a piece of A4 enables the most cost effective print. I think I ended up with three complete sets on a half piece.
Once you have it as a .pdf simply send it off to Precision Labels, tell them the colour you want and the opacity and a few days later you receive a decal sheet. I gave the area a couple of coats of clear gloss first to enable the best settling. The decals are particularly thin so tricky to manipulate when they are a good size but plenty of water, lay out the work area and think it through, apply plenty of water to the hull and you should get them in place easily enough. Softening and setting solutions allow them to settle perfectly and when they are given a final clear coating the backing is invisible.
I have created names for friends models as well as it is so easy to use fonts and sizing in Word to get a perfect name created. This was making the original paper template to ensure the fit.