The construction of the float decides heavily, the performance of the rotameter. In general, a float should be designed such that:
(a) it must be held vertical
(b) it should create uniform turbulence so as to make it insensitive to viscosity
© it should make the rotameter least sensitive to the variation of the fluid density.
A typical construction of the float is shown in fig. The top section of the float has a sharp edge and several angular grooves. The fluid passing through these grooves, causes the rotation of the float. The turbulence created in this process reduces the viscous force considerably.