comparing two identical equipments

designing models so that the result can be converted to prototypes

comparing similarity between design and actual equipment

hydraulic designs

ratio of inertial force to force due to viscosity

ratio of inertial force to force due to gravitation

ratio of inertial force to force due to surface tension

all the four ratios of inertial force to force due to viscosity, gravitation, surface tension, and elasticity

it is incompressible

it has uniform viscosity

it has zero viscosity

it is at rest.