Not that this is something I normally get excited about driving a Cherokee but I followed the thread and then tried it on the E6B function on my Palm Pilot.
That alleges (at 10 C) that Jet A has an SG of 0.82 (i.e 8.2 lbs / Imp Gal) Jet B an SG of 0.79 and Avgas 0.70.
It needs a temp of 45 C to get Jet A to 0.79 and -30 C to get to 0.85.
I don't suppose (for my purposes) that I need worry too much and I certainly haven't added anything to the thread but as an engineer (civil not aeronautical) this has exercised my brain somewhat - and I thank you all for adding to my store of knowledge.
DGG
