In book shelves a gain gives a better appearance than a dado.
A gain joint is laid out in the same way as the dado, except that the lines are not carried clear across the face of X, and only one edge is squared and gaged to the required depth.

Knife grooves are made in the waste for starting the saw as in the dado.

Before sawing, the blind end of the gain is to be chiseled out for a little space so as to give play for the back-saw in cutting down to the required depth.

To avoid sawing too deep at the blind end, the sawing and chiseling out of waste may be carried on alternately, a little at a time, till the required depth is reached.

It is easy to measure the depth of the cut by means of a small nail projecting the proper amount from a trial stick, Fig.251.The use of the router, Fig.