Instrumentation & Measurement Magazine 23-2 - 88

Coins as Measure of Size
Gerald Artner

oins are used as a measure of size in scientific publications. Over one hundred examples are collected.
Although standardized procedures for using coins
as a measure of size do not exist, use among scientists is so
widespread that some form of consensus has formed in the
community. Contemporary usage patterns of coins as a measure of size are analyzed qualitatively. Several rules and
predictions are formulated based on this analysis.

Measuring Size by Comparison
Photographs are widely used to depict prototypes in scientific
publications. To denote the size of an object in a photograph,
a variety of methods are common among scientists. Well
known objects have been used as comparison to give a rough
size estimate in photographs, e.g., pens [1], hands [2], playing
cards [3], matchboxes [4] and an iPhone 5 [5]. The placement
of these objects in photographs is no accident, e.g., one caption in [5] clearly states "Millimeter-wave radar for vital signs
monitoring prototype (dimensions comparison with iPhone
5)." These size comparisons are often insufficient. The object's size is then determined more precisely by performing
measurements. One technique is to measure lengths and add
dimensions later with image editing, e.g., [6]. A common
technique is to make the measurement procedure part of the
photographs by adding rulers (e.g., [7]) or objects of defined
known size such as cubes with a specified side length (e.g.,
cubes with a side length of 1 cm or 5 cm in [8] Figs. 2 and 11, respectively) and coins.
Most coins are of roughly the same size in the centimeter
range. This allows the concept of coins to be used as a rough
estimate of size, and indeed some authors advertise devices as
coin-sized [9]. However, the size of each specific coin is standardized. The use of a specific coin is therefore not only a size
reference as in coin-sized; it is a true measure of an object's size.
Of course, coin sizes can be converted to other well-known
measures of size, such as meter or inch; this does not appear to
be necessary, as coin sizes are well-known to everyone in the
community. Note, however, that coins are used as a measure of
size, but not as a measurement unit (see Rule 3).
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Over one hundred scientific publications are collected from
the field of electrical engineering which use coins as a measure of size. It is shown that this practice is used throughout
peer reviewed conferences, letters, magazines and journals,
and that it is widespread among publishers and countries.
Common practices for coin use are identified. Counterexamples to best practice are referenced if known to the author. The
coin measurement technique is developed further by giving
counterexamples to those rules, where no counterexample
was found in the literature. Several predictions are formulated
based on these qualitative investigations.

Coins Used as Measure of Size in
Scientific Publications
Over one hundred peer-reviewed scientific publications are
investigated for their use of coins as measure of size. It is not
the goal of this article to provide a quantitative description or
investigate an historical origin. The large number of scientific
publications containing photographs, in which coins are used
as a measure of size, shows that there is consensus among authors, reviewers and publishers, that coins are an acceptable
measure of size.
Samples were found and collected by browsing the literature as part of the author's regular reading and literature
research routines. The inclusion criterion is that a coin is used
as a measure of size in at least one figure in a paper that is published in a peer-reviewed conference, journal, or magazine or
in a scientific book. Papers were mainly collected from the areas of antennas and propagation and electrical engineering in
general as a consequence of the author's research interest. The
full list of investigated works with the shown coins and their
usage is available on IEEE DataPort [10].
Samples of coins used as a measure of size are collected
from all publication types in the antennas and propagation community (the number of included works are given in
brackets): conferences COMCAS (1), TELFOR (1), APS-URSI
(1), EuCAP (53), letters (19), magazines (3), transactions (10)
and books (2). They are collected from journals outside antennas and propagation: IEEE Micro (1), IEEE Microwave

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April 2020

Instrumentation & Measurement Magazine 23-2

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