I have a confession to make...
I confess that I do like to check out how this guy Paul Sellers does things, because while I am not generally one to follow a beaten path, and indeed more likely to fuck off into the underbrush and disappear... I do like how he explains his methods and reasoning. He's big on preserving and passing on a tradition of craftsmanship, but not hardcore "THIS IS THE ONLY RIGHT WAY TO DO THIS THING EVER" like you might expect a traditionalist to be.
Generally when I see something designed a certain way or styled in a particular fashion I make a point to avoid that general volume of the general designing phase space, and find it much more enjoyable when I am utterly unable to find something like what I made.
I did think the little dovetail markers Paul makes were clever though:
https://paulsellers.com/2011/12/making-the-paul-sellers-dovetail-template/I whipped up one of the usual "trace this outline" type of markers but it was really fiddly feeling, and I suspected the way Paul did his wouldn't have the same problem but a roughed out piece of scrap I experimented with made me realize I didn't like having to flip it back and forth to do both sides of the tails, and I didn't like having to peek behind it to make sure I had the spacing right, so I grabbed a different hunk of wood with a different shape hidden inside so I could rock it back and forth to do the same side angles, and started adding a window.
Then I cracked it with a careless chisel push... sat here bummed out and thinking for a good twenty minutes before I decided how to do it right, first with a big thick chunk of walnut and later after rethinking how to pass on the methods with a thinner piece of pine, and I'm pretty damn happy to say I can't find anything like them online.
Looking through the window lets you easily gauge the spacing, and the other side has a slightly different angle for the tails.
The greenish walnut one is 1:5 and 1:7, while the thinner pine one with the accidental pokeball knot is 1:5 and 1:8.
Laying the back of the v on top of the tail board gives you a square side to trace across, or you can put the v side against the back of a pin board and get the matching angles to go with your tails! The little pill bottle with cloth is full of MINERAL oil (do not use a drying oil like tung or linseed whatnot, they heat up and can combust) so I can just dab and spread it on my tool blades and finished workpieces, while the little bit of walnut with the screw and razor blade is a scraper, dragging it across a surface every couple of sandpaper steps (60 > 100 > scrape > 150 > 220 > scrape > 320 > 400 > finishing file) cleans any grit that may have been left behind and helps cut stray bits of grain fiber that was smushed down or standing up. Naturally the saws are my brass backed dovetail saw and steel backed carcase saw with their handles on a little square of walnut I was using to confirm the different angles/ease of using the markers.