Three parity pairs show the toy selection rule as checked bits. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
ground to middle checks the parity pair
The lower parity is even and the upper parity is odd. Different parities give allowed bit 1; matching parities give allowed bit 0. This row's computed bit is 1.
even→odd,allowed=1
middle to upper checks the parity pair
The lower parity is odd and the upper parity is even. Different parities give allowed bit 1; matching parities give allowed bit 0. This row's computed bit is 1.
odd→even,allowed=1
ground to upper checks the parity pair
The lower parity is even and the upper parity is even. Different parities give allowed bit 1; matching parities give allowed bit 0. This row's computed bit is 0.