A. Einstein’s work “On the Electrodynamics of Moving Bodies” [1, p.7-35] [5] [6, p.140-171], published in 1905, outlining the main provisions of the Special Theory of Relativity, is now deservedly considered classic. It is all the more important to detect and exclude typos and inaccuracies from it. Typos and inaccuracies can be purely stylistic, spelling, factual (dates, proper names, etc.) [4] and semantic [3]. The first three categories, of course, are not of great interest, although they are found both in reprints published during the author’s lifetime and in subsequent ones, but correcting them is only a technical task. Of greatest interest are semantic typos concerning inaccuracies in formulas, descriptions of experimental results, etc., since, in addition to correcting them, when discussing them, whole discussions arise that make it possible to determine whether the inaccuracy actually occurs, or whether the author’s intention is much deeper than the first glance. In addition, undetected or uncorrected inaccuracies can become a source of difficulties when teaching physics, in particular, the foundations of the Special Theory of Relativity based on primary sources, and also make it difficult to understand the author’s logic when studying them independently.

A preliminary search on the Internet, primarily in Russian-language sources, allowed us to find only one known published semantic typo concerning the incorrect indication of the speed at which the frequency, in the formula for the relativistic Doppler effect, reaches infinity [3]. Unfortunately, it is not enough to simply point out a typo, since, despite the passage of more than half a century, the above typo continues to appear in reprints of Einstein’s work [1, p.26] [6, p.161].

A. Einstein introduces the following procedure (criterion) to determine the synchronism of clocks A and B, located at different points in space A and B:

“For, suppose a ray of light leaves from A toward B at "A-time" $t_A$, is reflected from B toward A at "B-time" $t_B$, and arrives back at A at "A-time" ${t^{\prime }}_A$. The two clocks are synchronous by definition if ${ t}_B-t_A={t^{\prime }}_A-t_B "$ [1, p.9] [6, p.142].

And further, A. Einstein describes the result of a thought experiment demonstrating the relativity of simultaneity:

We further imagine that each clock has an observer co-moving with it, and that these observers apply to the two clocks the criterion for synchronism formulated in §1. Suppose a ray of light starts out from A at time ${\mathit{t}}_{\mathit{A}}$, is reflected from B at time ${\mathit{t}}_{\mathit{B}}$, and arrives back at A at time ${t^{\prime }}_A$. Taking into account the principle of the constancy of the velocity of light, we find that where $r_{AB}$ denotes the length of the moving rod, measured in the system at rest. The observers co-moving with the moving rod would thus find that the two clocks do not run synchronously while the observers in the system at rest would declare them synchronous.” [1, p.12-13, 6, p.145]

In our opinion, in the above quote there is a semantic inaccuracy; the preposition “not” is placed in the wrong place where it should be in meaning. The sentence in the quotation should read like this: “The observers co-moving with the moving rod would thus find that the two clocks do run synchronously while the observers in the system at rest would declare them not synchronous.”

To substantiate and prove the above, one should turn to the meaning of formulas (1), which determine how much time it takes for a ray of light to travel from the clock A installed at one end of the moving rod to the clock B installed at the other end of this rod and back.

If these times are equal, the clocks are considered to be running synchronously, that is, showing the same time, or having the same clock hands. Since the denominators of expressions (1) use the value of the rod speed v relative to a stationary reference frame, this speed cannot be determined by observers on the rod; for them, the time of passage of the rays from clocks A to B and back must always be equal, regardless of whether the observers move with the rod or the rod is at rest.

If it were possible for observers on the rod, by conducting one or another experiment, to determine whether the rod is moving translationally and uniformly, or at rest, this would be a violation of the 1st postulate of the Special Theory of Relativity, according to which there is no experiment that would show the difference between a system at rest and moving uniformly and rectilinearly. In other words, for observers on the rod, formulas (1) will always look like:

Consequently, only observers in a fixed, at rest coordinate system can calculate time using formulas (1).

It is they, and only they, who will be able to see how a beam of light from a source in clock A “catch up” with those moving away from it at the speed of movement of the rod v clock B, and will be able to notice the inequality in the time of the reverse movement of the beam from clock B to clock A, since in the latter case, clock A moves towards the ray of light released from clock B.

And, having clarified the inequality of these times, only observers from a system at rest will be able to draw a conclusion about the non-synchronism of the clock on the moving rod.

In our opinion, the presence of inaccuracy is quite obvious, however, we can briefly touch on possible objections [2]:

In our opinion, the presence of inaccuracy proved above is quite obvious. The more interesting question is why, for more than 100 years since the publication of A. Einstein’s seminal work, no one has yet paid attention to this inaccuracy and proposed to correct it, perhaps saving students and students studying primary sources from headaches and the impossibility of constructing a logically consistent presentation of one of the fundamental principles of the special theory of relativity.

As said over 50 years ago,“It seems appropriate with this letter to draw the attention of readers and, in particular, editors to the fact that reverence for the classics of science should not be extended to obvious typos made in the first publications of their works.” [3].

We join this statement.