yield stress, n - in solids, the maximum stress that can be applied without causing permanent deformation.
yield stress, n - in fluids, the shear stress required to initiate flow.
zero time (To), n - the travel time (correction factor), measured in seconds, associated with the electronic circuits in the pulse propagation system.
Z-score, n - standardized and dimensionless measure of the difference between an individual result in a data set and the arithmetic mean of the dataset, re-expressed in units of standard deviation of the dataset (by dividing the actual difference from the mean by the standard deviation for the data set).
Z'-score, n - measure similar to the Z-score except that the PT program standard deviation is replaced with one that takes into account the site precision of the laboratory. Z' is a valid approach when the laboratory's site precision standard deviation is less than the PT program (that is, these data standard deviation) or stated otherwise when the TPI > 1.
where:
Z' = site precision adjusted Z-Score,
Xi = laboratory's result,
X = PT average value,
s' = site precision standard deviation estimate, and
Sthese data = PT Program standard deviation estimate.