The U.S. Geological Survey has developed new standard rating tables for use
with Price type AA and pygmy current meters, which are employed to measure
streamflow velocity. Current-meter calibration data, consisting of the rat
es of rotation of meters at several different constant water velocities, ha
ve shown that the original rating tables are no longer representative of th
e average responsiveness of newly purchased meters or meters in the field.
The new rating tables are based on linear regression equations that are wei
ghted to reflect the population mix of current meters in the field and weig
hted inversely to the variability of the data at each calibration velocity.
For calibration velocities of 0.3 m/s and faster, at which most streamflow
measurements are made, the new AA-rating predicts the true velocities with
in 1.5% and the new pygmy-meter rating within 2.0% For more than 95% of the
meters. At calibration velocities, the new AA-meter rating is up to 1.4% d
ifferent from the original rating, and the new pygmy-meter rating is up to
1.6% different.