File talk:3-Pointer Altimeter.PNG
This image is factually incorrect. It attempts to show what a particular type of altimeter display would look like at about 10180 feet, but one portion of it is shown as if altitude was near sea level, not near 10000 feet.
The problem is in the "barber pole" striping below center of the dial. This is supposed to be fully visible at sea level, and become gradually covered by a rotating disc with a sector cut out of it as altitude increases. The "barber pole" section is supposed to be completely covered at about 16000 feet. So at 10000 feet, somewhat less than half of the barber-pole section should be visible.
In fact, the rotating disc is part of the "third hand" that would make one rotation every 100,000 feet. If you look at a good photo of this style of altimeter, for example the one contained in http://www.auf.asn.au/groundschool/umodule3.html, you can see that the third hand and the disc are really the same part and move together.
(You can also see that the inward-pointing triangle on the end of the third hand is contiguous with the rest of the hand; the current Wikimedia illustration shows the third hand with a "point" lying above the triangle where the third hand does not in fact end.)
The notes indicate that the diagram was originally taken from a FAA publication. I don't have a copy of that publication to check whether the error was in the FAA original, or was added when the SVG version was created. All of the images of this type of altimeter that I have found on the web show an altitude near sea level, which doesn't help demonstrate whether the disc rotates or not. However, I am a licensed private pilot and I know it does rotate as altitude increases. Here is a more authoritative reference as well: the book "Aircraft Instruments and Avionics for A&P Technicians", Max. F. Henderson, published by Jeppesen. Beginning near the end of page 15, it says
"The newer kind of three pointer altimeter seen in figure 1-25 has been modified to make it easier to read. The pointer that makes one revolution in 100,000 ft. has been extended to the outside of the face with a small triangle on the end so it cannot be covered up. In addition, a small window shows a striped pattern below about 15,000 ft. (at higher altitudes the striped symbol disappears)."
If someone would like to see Figure 1-25 from the book, email me and I'll scan the illustration.
Unfortunately, I am not an artist in the first place, and I lack tools that can edit vector illustrations. I cannot fix this illustration on my own. Is there someone else who could volunteer to fix it? I think it's important for Wikimedia content to be as accurate as possible. I know I have seen this particular illustration re-used somewhere outside Wikipedia.
