class MyData(NDData, NDArithmeticMixin):
    pass
x = MyData(16.0, uncertainty=StdDevUncertainty(4.0))
y = MyData(361.0, uncertainty=StdDevUncertainty(19.0))
z = x.add(y)
print(z)
print(z.uncertainty.array)
Propagation of uncertainties with Astropy