Why is Density Necessary in the Viscosity Comparison Method?

[thedy]

Hi,I don know if my question will be clear,but I will try it.So,I m wondering how was derive this equation:
viscosity=viscosity(known liquid)*density(known from table)*time(liquid will get over one point of Ubelohde viscometer to second point of viscometer(unknown liquid)/density(known liquid)*time(liquid will get over one point of Ubelohde viscometer to second point of viscometer(unknown liquid).
So once again in short form:viscosity*density*time/density*time.
So,I know it is a comparison method,that means density*time/density* time is undimensional and that means,that viscosity=density*time in this case.
And now my question:Why density in this equation?Why not only weight?Or why not to neglect density and count only time?Why is density necessary here?
Thanks for patient and widespread answer.

 

[Chestermiller]

In this viscometer design, apparently the viscosity times density times time for flow is a constant.