two sheets of 512 elements each, 16 × 32 (512 has no square side; 16 × 32 is the nearest, both powers of two), wrapped round a solid gold core. each sheet runs −+−+ as a chessboard: 256 + elements per sheet carry a nail poking out both faces. the outer tips face away; the inner tips press into the gold. the three layers weigh the same, 1% · 1% · 1%: 512 units each. press squeezes the stack from both sides: an outer tip that sinks comes out the inner face by the same amount, into the core. at 0.93 outside, the inner tips are 0.07 deep. ground PEWTER.