How do you measure your lens?

[Huck Finn]

After reading about the new Zeiss Ikon line on the internet, I noticed that Zeiss lists longer physical lengths for their lenses than Leica does for corresponding focal lengths in their specs. But when I went to PhotoPlus Expo in New York, I didn't notice much of a difference in most of the lenses that I saw.

So, I measured one of the ZI lenses at the expo. When I got home, I checked the ZI website. My measurements of the full length of the lens from bottom of the lens mount to front glass were the same. However, when I measured my Leica lens, the length from the Leica specs corresponded only to the portion of the lens that protrudes from the camera body, i.e. it didn't include the lens mount. I may have made an error in measurement, but I don't think so.

Oddly, when I measured my Voigtlander 75/2.5, it didn't correspond to either of the 2 measurements. The CV spec matched only the length of the lens protruding from the camera body (i.e. exclusive of lens mount like Leica) but with the lens hood attached.

I'm posting this to get a fact check from you folks & to see if anyone knows about the general industry practice in this respect. This seems like an important piece of information when making a purchasing decision especially if you're not in a position to look at 2 lenses side by side. Many of us value the compact size of our RF lenses, so accurate information is important.

Thanks for the help.