Homage to the Em Dash
How to use the em dash to improve readability.
It's not on your keyboard, but it is one of the most useful punctuation marks for allowing your reader to comprehend your meaning. This is especially true in technical writing which involves the necessity of accounting for every possible situation. That leads to run-on sentences and forces a reader to read a sentence multiple times in order to comprehend its meaning. By using the em dash to set off a parenthetical expression, or aside, we allow the reader to easily separate out side issues from the main meaning of the sentence.
Here is an example from my editing of a book on manufacturing floor automation. From the manuscript:
The “One Big Switch” conceptual model is only practical for control networks where the total number of devices plus an uplink port to the factory-wide network and a few spare ports is less than the available ports of an actual switch.
Here is my edited version:
The “One Big Switch” conceptual model is only practical for control networks in which the total number of devices—plus an uplink port to the factory-wide network and a few spare ports—is less than the available ports of an actual switch.
In the above case, we could also have achieved a similar effect by inserting parentheses, but the em dashes let the reader know beforehand that there will be breathing spaces in the upcoming text. The phrase "plus an uplink port to the factory-wide network and a few spare ports" is introduced merely to ensure that no important facts were overlooked. I treated the phrase as an aside. Metaphorically, we want to turn technical writing into a naturally flowing musical composition. In any case we cannot leave it to the reader to read, and then re-read a sentence, in order to figure out the hierarchy through trial and error. The reader will give up, if he has to do this repeatedly.
The em dash has further uses as a more emphatic replacement of the colon or comma in certain situations, but its use in setting off asides is of great utility in making complex situations intelligible on the first reading.
