Set the board, the number of tails and the slope. Watch the joint go together, then print the layout at full size, tape it to the wood and knife along the lines.
Measurements take decimals or fractions, like 3/4 or 5 1/2. The half-pin is measured at the narrow end, on the outside face. The full pins come out the same width there, which gives the fine-pinned look. Keyboard: focus the drawing, turn it with the arrow keys, Space knocks it together.
Shown here to fit. Printed, it is actual size, with a check square on every page so you can measure before you trust it. Crosses mark the waste.
| at the end | at the baseline |
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A dovetail is two boards cut to lock into each other, the flared tails on one and the pins on the other, so the corner cannot pull apart in the direction it is loaded. It has held drawers and chests together for a very long time, and most people remember the first one they cut, usually for the gaps.
Layout is the part that decides whether it fits. Put in your board and choose the slope. A common starting point is about 1:6 for softwoods and 1:8 for hardwoods, but those are habits, not rules, and plenty of good work sits either side. Then print the template, check the square with a ruler, and knife your lines. The drawing turns if you drag it, and the knock is free.
Saw on the waste side of the line. The crosses are there so you remember which side that is.