Wikipedia fills us in on some of the details of this sans-serif medium-weight grudge match:
Akzidenz is sometimes at first glance mistaken for the Helvetica or Univers typefaces. The similarities of Helvetica and Akzidenz are apparent, but the subtle differences include the uppercase and lowercase C, and the uppercase G. J, R., and Q. Aside from the subtle differences in these individual letters, Miedinger’s primary change to Akzidenz is Helvetica’s higher x-height, the distance from the baseline to the height of the lowercase letter x. The general effect is that Helvetica appears more oblong while Akzidenz maintains circular counters and bowls. Both Helvetica and Univers are more regular and have a greater consistency of stroke weight.
Helvetica also has an unofficial movie on youtube, lovingly called helveticake by a commenter. Arial has no video representation, and most typographers would tell you that’s how it should be.
Thanks to Pedro Serro at Type for you for finding this.