PS is the US Army's preventative service magazine, something for the soldiers to read while on CQ duty or waiting for the wash rack to open up
![Wink ;) ;)](data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7)
. It is free and online for back issues, there is a link somewhere.
On glow plugs, not only is cold resistance important, also time to heat and dynamics. The PS excerpt is a bit off for us civvies since we may not have exact replacements and using odd plug or two could cause issues if resistance isn't the same between plugs. One could overheat while another doesn't get warm enough.