  We introduce a class of monotone $\sigma$-complete effect algebras, called
representable, which are $\sigma$-homomorphic images of a class of monotone
$\sigma$-complete effect algebras of functions taking values in the interval
$[0,1]$ and with pointwise defined effect algebra operations. We exhibit
different types of compatibilities and show their connection to
representability. Finally, we study observables and show situations when
information of an observable on all intervals of the form $(-\infty,t)$ gives
full information about the observable.
