What is a Shift-adjusted rating?

Shift-adjusted rating:
Stage-discharge relationships (ratings) are primarily developed from a graphical analysis of multiple streamflow measurements. Measurements are generally made on 8-week intervals. The frequency/interval of streamflow measurements may change based on a variety of circumstances including (but not limited to) flow conditions and rating definition. All discharge measurements are compiled and maintained in the USGS NWIS database. Each measurement is made according to established USGS guidelines and undergoes quality assurance review. Some measurements indicate a change in the rating, often due to a change in the streambed (for example, scour or deposition) or growth of aquatic vegetation. Such changes, called "shifts," may indicate a short- or long-term change in the rating for the gage. When indicated by a streamflow measurement, the shifts are applied mathematically as temporary adjustments to a defined rating.
The tables being provided are shift-corrected. The indicated shift has been applied to the base rating. The shift adjustments are applied to the rating as streamflow measurement data becomes available, resulting in an adjusted rating. Some ratings may change as often as weekly, others may not change for months or years.