Talk:Perm (unit)

disclaimer

 * I'm certainly no expert in this subject. I started the article because WP's coverage was lacking and it was a convenient place to summarize what I was learning. Thanks for helping correct my rookie mistakes. --Dystopos 21:42, 13 August 2007 (UTC)

Precision of conversion factors
I don't see the point of stating the conversion factor between US and metric perms to 10 significant digits, especially since that is still not an exact value. Perms (of both kinds) are used primarily in engineering, in contexts where even 3 significant digits would normally be plenty. I included 6, mainly for consistency with all the other figures in the article. If anyone insists on reverting back to 10 digits, at least please use the correct number: 1.517346264, not 1.517436264. Thanks, Hqb (talk) 17:26, 8 December 2007 (UTC)
 * Fair enough, if anyone wants a more accurate figure, let them calculate it but that "equivalent" wording's got to go. -- Jɪmp 17:53, 8 December 2007 (UTC)
 * Done. (The parenthesized sentence fragments looked grammatically iffy, anyway.) Hqb (talk) 18:13, 8 December 2007 (UTC)
 * How about a table? Here are the conversions I calculate (assuming 13.5951 g/cm³ for Hg & 9.80665 m/s² for gravity).


 * 1 metric perm ≈ 86.81268239 ng/sm²Pa ≈ 1.517346264	US perms
 * 1 US perm ≈ 57.21349467 ng/sm²Pa ≈ 0.65904535 metric perms
 * 1 ng/sm²Pa ≈ 0.011519054 metric perms ≈ 0.017478394 US perms


 * Jɪmp 19:08, 8 December 2007 (UTC)

I think we have the wrong exponent in the conversion of the SI perm to US perms. The article currently says that 1 SI perm "≈ 1.74784x10+10 US perms". I think this should be 10 to the -10, rather than + 10. If I'm right, then the current value is off by roughly 20 orders of magnitude. In addition, most other Wikipedia pages use superscripts to show exponents, which I'm not sure how to enter into the text. However, I think superscript exponents would be clearer.

It would be useful to mention "Imperial Perms" somewhere in the calculations. I haven't found any web pages that mention both "Imperial Perms" and "US Perms". Pages mention one or the other. I think they are the same, but I didn't find a page that specifically makes that statement.

DIN conversion
How are we converting the DIN unit (and does it have a name) to US perms when they are not dimensionally equivalent (there's no pressure factor in the DIN unit)? I assume we're assuming US perms at the given standard pressure, if so this should be made clear. Jɪmp 18:26, 8 December 2007 (UTC)
 * I've hopefully clarified it a bit. See the cited source for full details. Hqb (talk) 19:10, 8 December 2007 (UTC)