A conservation ledger pins the angular momentum to a cited source both before and after a state change, so the before and after values can be checked against each other. The bookkeeping is exact only for the stated inertia, angular speed, and before/after states in the ideal rigid-body model. Real systems add distributed-mass geometry, friction/torques, axis alignment, sensor calibration, finite precision, and measurement uncertainty.
The conservation claim binds to the intended before and after ledger. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
The conservation ledger pins the exact before and after case
The ledger compares the 6 to 3 inertia change only with spin 4 to 8.
6×4=3×8
The before and after sources are part of the claim
The value 24 comes from both rendered products, not from a caption alone.