The SPT will indicate a signal strength between 0 and 10 (The SPT display will indicate 10 as an "A" ). 0 being the lowest signal strength, 10 (A) the highest.
Whilst Signal is a service level guide it is not a true indication of service availability, it is a transitory indicator. Therefore the reading should (ideally) be compared with circuit availability coupled with signal strength. WebWayOne systems record both Signal and Circuit Availability.
WebWayOne recommend that signal strength readings of up to and including 3 should be considered for an antenna upgrade.