In most cases a parameter, eg Y, is not measured directly, but is
determined from
N
other input quantities
X
1
,
X
2
,
….
,
X
N
, through a functional relationship
f
:
The input quantities
X
1
,
X
2
, ...,
X
N
are – of course – also subject to
probability distribution.
1 2
N
Y f ( X , X ,.....X )
Combined uncertainty