Uncertainty in measurements.

[Albert Chan]

Uncertainty in measurement calculations may be affected by variables dependency.

Example: a = b = -4 to 6 = 1 ± 5

a - b = ±10 (if variables totally independent of each other)
a - a = 0

a * b = -24 to 36 = 6 ± 30
a * a = 0 to 36 = 18 ± 18