[Ram2020]

I am measuring the flow rate of liquids, water and various dyes through different types of filter papers. I am having the trouble about how to do it?

Simply dipping a filter paper in a dye and measuring its length isn't working. I am supposed to click pictures of the motion of dye in every minute for five minutes and find the velocity. But I don't know how to do measure the length without taking it out of the solute solution. Any help is welcome.