With fixed radius-cubed, only the matching period-square preserves the normalized ratio. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Right period-square row 1
The right radius-cubed is fixed at 64. Right period-square 32 gives the checked right ratio.
rB3TB2=32/64=21,a=1
Right period-square row 2
The right radius-cubed is fixed at 64. Right period-square 36 gives the checked right ratio.
rB3TB2=36/64=169,a=0
Right period-square row 3
The right radius-cubed is fixed at 64. Right period-square 40 gives the checked right ratio.
rB3TB2=40/64=85,a=0
Only one right-period row matches the normalized constant
The helper keeps the two radius-cubed sources fixed. The scan changes only the right period-square, so one-half accepts and nearby ratios reject.