[SML] Butt board schematic

[Dougherty, Jim]

To the good suggestions already made, I¹d add:

- Incorporate a slight curve in the edges of the plywood, so that it fits
better onto the seats and leaves leg room (especially if it¹s long);

- Add a means of keeping it on the seats¹ arms - ours has bungies with a
plywood toggle that fit into the gaps between seats.  This way scooting
forward doesn¹t result in a grand tip-over.

- Jim Dougherty
ATD Middlebury College Theatre Dept.