# Calculating the Equivalent Radius

Comparing the minimal frictional coefficient with results from a Sedimentation Velocity experiment will yield estimates of maximum hydration and maximum asymmetry. Please note that this comparison depends on the description of the buffer, particularly the viscosity, η, of the buffer; therefore accurate results may require that you enter or interpolate a viscosity since the default viscosity is that of water. Sednterp calculates these estimates using the models of prolate, oblate, and cylinder for the asymmetry. Since hydration and asymmetry are related, only maximum values can be given from sedimentation experiments alone. However, if some information is available about either hydration or asymmetry then Sednterp will use this to calculate better estimates of the other value. For instance, if the composition is used for an estimate of hydration, you may check a box to use this estimated hydration to calculate a better estimate of the asymmetry.