The MOS value that appears on your charts and graphs is not calculated by IPSLA Manager. It is a value acquired from the codec on your VoIP network.
MOS is an industry standard measure of call quality expressed on a scale of increasing perceived quality, from 1 to 5. MOS is computed by a standard International Telecommunications Union (ITU) algorithm involving the codec for your VoIP network and values of latency, jitter, packet loss, and MOS advantage factor. Jitter, latency, and packet loss are variable quantities that are measured by IP SLA Manager in realtime.