text: * Due to its reliance on the ability of the fluid or gas to displace the float, graduations on a given rotameter will only be accurate for a given substance at a given temperature. The main property of importance is the density of the fluid; however, viscosity may also be significant.  Floats are ideally designed to be insensitive to viscosity; however, this is seldom verifiable from manufacturers' specifications.  Either separate rotameters for different densities and viscosities may be used, or multiple scales on the same rotameter can be used.
  *Because operation of a rotameter depends on the force of gravity for operation, a rotameter must be oriented vertically. Significant error can result if the orientation deviates significantly from the vertical.
  * Due to the direct flow indication the resolution is relatively poor compared to other measurement principles. Readout uncertainty gets worse near the bottom of the scale. Oscillations of the float and parallax may further increase the uncertainty of the measurement.
  * Since the float must be read through the flowing medium, some fluids may obscure the reading. A transducer may be required for electronically measuring the position of the float. 
  * Rotameters are not easily adapted for reading by machine; although magnetic floats that drive a follower outside the tube are available.
  * Rotameters are not generally manufactured in sizes greater than 6 inches/150 mm, but bypass designs are sometimes used on very large pipes.