Staff members at the Securities and Exchange mission have parceled out a new bit of XBRL guidance by adding another Q&A to their staff interpretations and frequently asked questions on interactive data disclosures.

The SEC’s Office of Interactive Disclosures focused this time on units of measure and how they are used in interactive data filing. Those staff members apparently are seeing nfusion, so they thought it might helpful to explain for the benefit of all who are dealing with XBRL filings.

Depending on the element or tag in the taxonomy that is selected and the amount that is being reported, every amount expressed in an XBRL submission is linked with three things: an “XBRL item type,” an underlying “data type,” and a “unit,” or unit of measure. A mmon XBRL item type such as “Moary” can be further described with a data type, as in a “Non Negative Moary” data type, which excludes negative amounts.

Typically, that is still not enough to mpletely define a given amount that a mpany might need to report in its financial statements. That’s where units me into play. Data types use unit types to further define or characterize the information that is being reported. In many cases, the unit is US dollars, but it might also be megawatts, millions of barrels, millions of bushels, or employees.

The staff explains that the “Pure” XBRL item type is used most frequently with elements that describe percentages, rates, and ratios, and it is used most frequently with the “pure” unit. But here’s where the staff has seen some nfusion. The SEC is having a hard time mprehending how the pure unit uld be used to describe any item type other than the pure XBRL item type, and it can’t see how the pure unit makes sense with anything other than ratios, rates, or percentages.

So here’s the staff’s advice: if you’re thinking of using the pure unit with anything other than a pure XBRL item type, and if you’re thinking of using the pure unit with anything other than a ratio, a rate, or a percentage – don’t do it.

The staff says a standard units registry is expected to be provided in a future version of the Document and Entity Information Taxonomy to further refine direct selections. In the meantime, the filers should select the unit type that most closely fits the item and data type. The Q&A guidance also provides a table showing some mmon associations among XBRL item types, data types, and units.