Displaced volume drives apparent weight down to the float threshold. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Small displacement leaves eighty newtons
Displaced volume V=1 cubic metre gives buoyant force 20 newtons. From weight 100 newtons, the support reads 80 newtons.
100−20=80
More displaced fluid lowers the reading
Displaced volume V=3 cubic metres gives buoyant force 60 newtons. From weight 100 newtons, the support reads 40 newtons.
100−60=40
At full balance the support reads zero
Displaced volume V=5 cubic metres gives buoyant force 100 newtons. From weight 100 newtons, the support reads 0 newtons.