In hydrometer analysis for a soil mass

In hydrometer analysis for determining the particle size distribution of a soil mass, corrections are made to the hydrometer readings to account for the effects of the meniscus and the dispersing agent. Here's how these corrections are typically applied:
Meniscus Correction: The meniscus correction is usually subtractive because the hydrometer reading is taken at the bottom of the meniscus in the graduated cylinder. This correction accounts for the surface tension effect that causes the liquid to curve up the walls of the cylinder.
Dispersing Agent Correction: The dispersing agent correction is usually additive because the dispersing agent can change the density and viscosity of the liquid, thereby affecting the hydrometer readings. This correction accounts for the additional mass and volume introduced by the dispersing agent.