Referencing Figures in Technical Documents

Charles R. Sullivan
April 22, 2002

In a technical document, every figure (or table) should be referenced in the text.  There are several common phrases used to do this.  It might seem to matter little which phrase one uses, but the differences can matter.  Several correct and incorrect options are reviewed here.  Incorrect or undesirable examples are distinguished by being set in italics.

One of the most common useful and correct ways to reference a figure is with “as shown in.”

Our new design has an inductor connected in series with a capacitor, as shown in Fig. 1.


“As can be seen in” might appear be used almost interchangeably in the technical literature.  However, the meaning is subtly but importantly different.  “As shown in” means that the author(s) have constructed a figure to illustrate what they are talking about.  “As can be seen in,” on the other hand, would be used to reference a figure in which there is raw data, from which the authors make the observations they are discussing; the reader is invited to make the same observations.  For example:

We expected a sharp dip in impedance near the resonant frequency, but we also measured a sharp peak in impedance a higher frequency, as can be seen in Fig. 2.  This indicates an additional resonance, which we attribute to resonance of the inductor with its parasitic capacitance.
Sometimes people also write “as seen in.”  This could be construed as a shorter version of “as can be seen in” with the same meaning, but I think it results most often from an inadvertent cross between the two familiar phrases, and I prefer to avoid it.  I’d be interested to hear if there are situations in which it makes more sense than the other options.

Another possibility is to simply put the figure number in parentheses at the end of the sentence, or after the item that has been described.

Our new design has an inductor connected in series with a capacitor (Fig. 1).

Impedance measurements (Fig. 2) and transient response measurements (Fig. 3) confirm behavior as expected, except for the unexpected high-frequency peak observed in Fig. 2.

It is also possible to similarly set off the figure number with commas:
The plot of impedance measurements, Fig. 2, shows an unexpected high-frequency peak.
However, to do this correctly and have it make sense, the corresponding phrase must also describe the figure.  For example, this would be incorrect:
 An unexpected high-frequency peak, Fig. 2, was found for the series circuit.
Fig. 2 is “the plot of impedance measurements,” but it is not “An unexpected high-frequency peak.”

Sometimes the readers are told to “see Fig. 3.”  That’s OK, but it is more polite to say what is available in the various figures, and let the readers decide for themselves what to look at.  If you use “see Fig. 3,” keep in mind that it is a complete sentence.  Thus, the following is not grammatically correct, because it consists of two sentences joined only by a comma:
 

An unexpected high-frequency peak was found for the series circuit, see Fig. 2.


The grammatical problem could be removed by instead using any of the following:

An unexpected high-frequency peak was found for the series circuit.  See Fig. 2.

An unexpected high-frequency peak was found for the series circuit; see Fig. 2.

An unexpected high-frequency peak was found for the series circuit (see Fig. 2).

But even thought those are grammatically correct, they are somewhat awkward.  It is better to avoid telling the reader what to do anyway, unless the imperative is integrated into the text, as in this example:
For an illustration of this surprising behavior, see Fig. 2.