The block's 7.5 in side runs across the bridge (as drawn) and rests on both top chords, each seated at least 1/4 in inside its ends.

Other reading: 7.5 in along the span, resting on a transverse beam.

The top chords peak at mid-span, so the block seats at the centre rather than rocking on an off-centre high point.

Other reading: Any top profile the block can sit on.

The tunnel floor is the deck surface (top of the floor system), and the deck is level.

Other reading: The tunnel floor is the very lowest point of the bridge, which would forbid floor beams there.

'Laminated with any substance' means a surface coating; members built from several sticks glued together are allowed.

Other reading: No member may be several sticks glued together.

Gussets are allowed if cut from the supplied sticks (edge-glued 1/8 in plates). The rules set no size limit; we cap them at 2 in.

Other reading: No gussets at all.

The bridge reacts at the gap edges (x = +-6 in), the conservative span, and bears at least 1/4 in onto each abutment.

Other reading: Reaction spread over the bearing length.