  In papers on cold field electron emission from large area field emitters
(LAFEs), it has become widespread practice to publish a misleading
Fowler-Nordheim-type (FN-type) equation. This equation over-predicts the
LAFE-average current density by a large highly-variable factor thought to
usually lie between 1000 and 1000 000 000. This equation, although often
referenced to FN's 1928 paper, is a simplified equation used in undergraduate
teaching, does not apply unmodified to LAFEs, and does not appear in the 1928
paper. Technological LAFE papers often do not cite any theoretical work more
recent than 1928, and often do not comment on the discrepancy between theory
and experiment. This usage has occurred widely, in several high-profile
American and UK applied-science journals, and in various other places. It does
not inhibit practical LAFE development, but can give a misleading impression of
potential LAFE performance to non-experts. This paper shows how the misleading
equation can be replaced by a conceptually complete FN-type equation that uses
three high-level correction factors. One of these, or a combination of two of
them, may be useful as an additional measure of LAFE quality; this paper
describes how to estimate factor values using experimental data. Suggestions
are made for improved engineering practice in reporting LAFE results. Some of
these should help to prevent situations arising whereby an equation appearing
in high-profile applied-science journals is used to support statements that an
engineering regulatory body might deem to involve professional negligence.
