How does BayesiaLab calculate the Means and Values in the Monitors? What is the difference?
For each node that has values associated with its states, an Expected Value $v$ is computed by using the associated values and the marginal probability distribution of the node $$v = \sum_{s \in S} p_s \times V_s$$ where $p_s$ is the marginal probability of state $s$ and $V_s$ is its associated value. 
This Expected Value is displayed in the monitor.

When new pieces of evidence are set, a the delta value is displayed in the monitor:
This delta is the difference between the current Expected Value v
and:
