Where does recession collide?

G. K. Gilbert's 1907 Rate of Recession of Niagara Falls measured how the crest of the falls had moved upstream year by year as the plunging water wore back the rock. In geomorphology recession names the gradual retreat of a landform, such as a waterfall crest, a sea cliff, a shoreline, or the front of a glacier, as material is removed from its edge. It is reported as a distance moved per unit of time, for example metres per year of cliff or ice-front retreat. This referent is a physical edge moving across the land, and it has nothing in common with a fall in national output or the baring of a tooth root beyond the shared word.[1]

Unit

A landform edge retreating, in distance per year

Recovery means

A glacier front can readvance in colder periods, though eroded cliff and waterfall retreat does not reverse

Measured by

Surveyed by repeat mapping, dated shorelines, or aerial and satellite comparison of edge position over time

Arthur F. Burns and Wesley C. Mitchell's 1946 Measuring Business Cycles set out how to date the phases of the business cycle, marking the contraction that runs from a peak in activity down to a trough. In macroeconomics a recession is that contraction phase: a decline in output, employment, income, and trade that is broad across the economy and lasts more than a few months. In the United States a committee at the National Bureau of Economic Research identifies each recession by its peak and trough months. This referent is a downturn in a whole economy, tracked in output and jobs, not the retreat of a landform or the loss of gum around a tooth.[2]

Unit

A peak-to-trough contraction of a whole economy

Recovery means

A recession ends at a trough, after which activity expands again in the recovery and expansion phases

Measured by

Dated from broad activity indicators such as output, employment, real income, and sales, as by the NBER dating committee

W. J. Gorman's 1967 Prevalence and Etiology of Gingival Recession surveyed how often the gum margin sits below its normal position and what drives it there. In periodontology gingival recession is the movement of the gum margin toward the root tip, which exposes the root surface of the tooth and can follow toothbrush trauma, thin tissue, or periodontal disease. Miller's 1985 classification of marginal tissue recession later grouped cases by how far the gum and bone loss extends, and it is still widely used. This referent is soft tissue withdrawing from a single tooth, measured in millimetres of exposed root, not a shrinking economy or a retreating cliff.[3][4]

Unit

Gum margin displaced toward the root, in millimetres of exposed root

Recovery means

Lost gum tissue may be rebuilt by grafting procedures, though it does not regrow on its own

Measured by

Measured clinically in millimetres from the cementoenamel junction to the gum margin, and graded by Miller's classification