  Using a one-to-one correspondence between observables and their spectral
resolutions, we introduce the sum of any two bounded observables of a
$\sigma$-MV-effect algebra. This sum is commutative, associative and with
neutral element. Under the Olson order of observables, the set of bounded
observables is a partially ordered semigroup, and the set of sharp observables
is even a Dedekind $\sigma$-complete $\ell$-group with strong unit.
