ob·serv·a·ble 
(əb-zûrvə-bəl)
(əb-zûrvə-bəl)adj.
1. Possible to observe: observable phenomena; an observable change in demeanor.
2. Archaic Deserving or worthy of note; noteworthy: an observable anniversary.
n.
A physical property, such as weight or temperature, that can be observed or measured directly, as distinguished from a quantity, such as work or entropy, that must be derived from observed quantities.
ob·serva·bly adv.