The second issue that is addressed in the present section is dimensional analysis. It is advisable to list all the relevant quantities that play a role in the experiment and subsequently reduce them to dimensionless form. Several advantages can be derived from this step. These are: 

    1.  A reduction in the number of variables,
    2.  Development of a statement of the similarity principles
    3.  Independent variables such as length and time adopt values close to unity.

Reconsider the example of measurement of drag. To cover all possible cases one must write drag D in functional form as

where  is the vehicle speed,  and  are its transverse and longitudinal length scales, and  and  are density and viscosity of seawater, respectively. Various strategies are available for casting equations such as the one for drag in dimensionless form.