  In field electron emission (FE) studies, to interpret current-voltage data
and extract characterization parameters, we use smooth planar metal-like
emitter (SPME) methodology and a data-analysis plot. Three types exist:
Millikan-Lauritsen (ML), Fowler-Nordheim (FN) and Murphy-Good (MG) plots. In
SPME methodology, ML and FN plots are slightly curved but a MG plot is nearly
straight. 1956 MG FE theory is better physics than 1928 FN theory, so we expect
MG plots to be more precise than ML or FN plots. Current-voltage data are often
converted: measured voltage to (apparent) macroscopic field, current to
macroscopic current density. Thus, four different data-input forms exist.
Over-simplified models of system behaviour are widely assumed. Whether simple
use of a data-analysis plot is a valid interpretation method is often
neglected. Published FE studies seem to contain a high incidence of spurious
values for "field enhancement factor". A procedure (the "Orthodoxy Test")
described in 2013 allows a validity check: around 40 % of a small sample of
results were spuriously high. To assist data interpretation and validity
checks, a simple user-friendly webtool has been designed by the lead author. As
inputs, this needs system specification data and "range-limits" data from any
of the three plot forms, using any of the four data-input forms. The webtool
then applies the Orthodoxy Test, and -- if passed -- extracts characterization
parameters. This study reports: (1) systematic tests of webtool functionality,
using simulated input data prepared using Extended MG FE theory; and (2)
systematic comparisons of the three different data-plot types, to check how
well extracted parameter values match simulation input values. A summary review
of relevant theory is given. For formal emission areas, the MG plot performs
better than FN and ML plots. This is important for FE science.
