# Simple Fluid statics doubt

According to the law of floatation when a body of surface area S is floating the liquid with density $\rho$ then

Weight of the body =weight of the displaced liquid. But why don't we count the force due to the atmospheric pressure here making it

Weight of the body + $P_0S$=weight of the displaced liquid.

I have started learning fluid dynamics hence please don't find if its a very foolish question.

Because if the pressure at the surface if the liquid is $P_{\rm atmosphere}$ and the pressure below the surface of the liquid is $P_{\rm atmosphere + liquid}$ then for the upthrust you are interested in the difference in pressure due to the liquid at the bottom and top of the submerged part of the floating body.$\Delta P_{\rm liquid}$ which is $P_{\rm atmosphere + liquid} - P_{\rm atmosphere} = \Delta P_{\rm liquid}$.