This discussion of displays was touched on in another Tech Log thread, and with your permission, I'll cross-post a snippet:
Originally Posted by
DozyWannabe
As far as primary flight instruments go, a bit of Google-bashing drew my attention to a seminal 1949 report for the Journal of Applied Psychology by one Walter F. Grether - probably the best retrospective can be found at this link:
http://repository.asu.edu/attachment...010N_11979.pdf
However, further supporting info on the study can be found with a Google search on "Grether 1949 altimeter".
The gist of the findings was that the traditional three-pointer dial design proved to be by far the most susceptible to misreads, and the optimum dial design used a single pointer with a dual-drum digital counter (which I'm guessing evolved into the combination drum/pointer altimeter that later became nearly ubiquitous prior to the advent of the PFD). The study also noted, however, that the vertical "tape" design (at a concept/experimental-only stage at the time of the report) was very close in terms of speed of reading and not far off in terms of reading accuracy.
It's worth reading through the article linked above, as it gives a very useful precis of how the modern civil PFD evolved, and some very interesting background info on the primary design considerations - the short version being that, as ever, it was a compromise.
Originally Posted by
DozyWannabe
As an aside, I dug up this image which purports to be a real A330 PFD:
As you can see, at FL400 the most significant three digits are emphasised on the numerical display, and because of this emphasis it should be fairly easy to determine that the numbers are winding down (even more obvious in concert with the "tape" and the V/S pointer).