But our tolerance level to, say, changes in our core body temperature could well be, for hyperthermia, +/+ plus 10% to plus 15%, or for hypothermia, -/- minus 10% to minus 15%
And I'm the one in need of an education?
Textbook human core temperature is 310K. A 10% increase gives 341K. A human at 310K is a dead human.
Of course, we should be using the Kelvin scale (or any absolute scale), unless of course you think that 100°C is twice as hot as 50°C (which raises the interesting question "is 0°C twice as hot as 0°C and 1°C infinitely hotter than 0°C")
I don't think I have ever come across the use of "million" or "billion" in any scientific documentation I have read or written. I suspect they do come up in discussion of the ever-problematic units of volume, where there could be semi-legitimate discussion of millions or billions of cubic metres where the correct way of dealing with the problem is to talk about cubic kilometres. Only a cubic kilometre implies 1000 cubic metres to the uninformed, out by six orders of magnitude, and is thus capable of causing confusion to the scientifically illiterate.
"Billion" in Germany is now in common use as 10^9, but only in English. In German "Milliard" is 10^9, and "Billion" simply never comes up that I am aware of, but you are more likely to hear these in a business discussion than a scientific one.
Anyone using "billion" "trillion" etc. here had better be aware of the ambiguity and be prepared for their bid for some company or other to cost them 1000 times what they were hoping to pay.