error propagation
dec-02
x, a, b, c = numbers
sa, sb, sc = corresponding uncertainties
sx = uncertainty we want to calculate

1. x = a+b-c
	sx = sqrt(pow(sa,2)+pow(sb,2)+pow(sc,2))
2. x = a*b/c
	sx = x*sqrt(pow(sa/a,2)+pow(sb/b,2)+pow(sc/c,2))
3. x = pow(a,b)
	sx = x*b*(sa/a)		[assuming sb=0]
4. x = log10(a)
	sx = 0.434*(sa/a)
5. x = log(a)
	sx = sa/a
6. x = pow(e,a)
	sx = x*sa
7. x = f(a, b, c, ...)
	sx = sqrt(pow((df/da)*sa,2)+pow((df/db)*sb,2)+pow((df/dc)*sc,2)+...)
	(d = partial derivative)

ref:
http://science.widener.edu/svb/stats/error.html
http://www.rit.edu/~vwlsps/uncertainties/Uncertaintiespart2.html
http://lectureonline.cl.msu.edu/~mmp/labs/error/e2.htm