Density changes pressure while depth and gravity stay fixed. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.
highlighted = computed this step
Light fluid gives thirty pascals
Depth h=3 m and gravity g=10 metres per second squared stay fixed. Density rho=1 kilogram per cubic metre gives pressure 30 pascals.
ΔP=1×10×3=30
Double density doubles the pressure
Depth h=3 m and gravity g=10 metres per second squared stay fixed. Density rho=2 kilograms per cubic metre gives pressure 60 pascals.
ΔP=2×10×3=60
Dense fluid triples the light reading
Depth h=3 m and gravity g=10 metres per second squared stay fixed. Density rho=3 kilograms per cubic metre gives pressure 90 pascals.