\myheading{Fencepost error / off-by-one error}

Here's yet another illustration of such errors.

You are riding by metro/tram/bus and your friend asking you,
"how many stations/stops shall we pass before your the destination station?"

For people striving for accuracy and exact sciences in general, such questions are like scraping a chalkboard.
It is even worse if, at the moment of the question, the train/tram/bus is at a stop.

To answer such a question, you need to clarify --- shall we count stops at stations or passings between them?
Do we take into account the current stop and/or the final one?

Without answers to these questions, such errors appear.

Also, an example from Kurt Vonnegut's Cat's Cradle, the very beginning of the book:

\begin{framed}
\begin{quotation}
When I was a younger man--two wives ago, 250,000 cigarettes ago, 3,000 quarts of booze ago.
\end{quotation}
\end{framed}

Go figure, how many ways there are exist to determine that point in time ("two wives ago").
Considering that Kurt Vonnegut at the moment of writing was 1) married; 2) not married.

Also, often, a phrase in advertisement like "... [something] is valid from January 10th to 20th".
Without the addition of the word "inclusive", it is not clear if January 20th is included in this interval or not?
Is this a half-closed interval or a closed interval?

See also:
\url{http://www.catb.org/jargon/html/O/off-by-one-error.html},
\url{http://www.catb.org/jargon/html/F/fencepost-error.html}.

Now an excerpt from the amusing article by Denys Wilkinson:

\begin{framed}
\begin{quotation}
Communications direct to the projectionist are always good and should be made in such a manner that it is not immediately clear whether the Slidesman is addressing the projectionist or the audience. Absurd complication in the instructions must be avoided. The Slidesman uses something like: ‘After the next slide but two I shall want to look again at the last one but four.’ After the next slide: ‘I meant of course that slide which was then going to be the last one but four after I had indeed had that which was going to be the next but two, not that which was then the last but four.’ Follow this by skipping one slide.
\end{quotation}
\end{framed}

[His article can be found in \textit{A Random Walk In Science --- Eric Mendoza}\footnote{\url{https://archive.org/details/EricMendozaEd.ARandomWalkInScience_201406/}}.]