Like the Parshall Flume upon which it is based - under laboratory conditions Montana Flumes can be expected to operate accurately to within +/-2%. 

To achieve optimal accuracy:

• The site must be suitable for the flume
• The incoming flow must be well conditioned
• The flume must be installed accurately
• The flume and upstream / downstream channels must be kept clear of vegatative growth, trash, debris, and silt
• The interior flow surfaces must be kept clean and free of algal growth and corrosion
• Downstream conditions should not submerge the flume

​In practice, accuracies better than +/-5% are difficult to achieve and total system accuracies (flume, flow meter, etc.) are typically +/-10%.