Someone commented that she has was doing a lot of math — what is 3 3/16 minus 1/2 anyway??? — since beginning to use SketchList 3D. I explained that much of the time you are sizing and placing boards — the math is automatic and needs no thought really. I put together a 3 minute video about how to do this. If you want to butt two boards together you simply make the correct sides (left, right) equal.
The dimension boxes work on a diagonal. When Right of Board A = Left of Board B – the boards butt together. The right edge of Board A touches the left edge of Board B. To place Board B between A and C – make sure the right edge of Board B = the Left edge of Board C. And since the left and right edges of board B should always be different – clicking the Width column heading will change the width of board B to be EXACTLY what is needed to fit between the two boards. Which if you are dealing with 11 7/8 and 25 5/16 – does in fact eliminate some math for you. This is one thing woodworking design software should do.
It really is harder to read about than to watch. See the video by clicking here.