The intent of this method is two-fold. First to provide a way to verify the integrity of the instance's data after deserialization. If someone (or something) modified the serialized values then CalculateChecksum should return a different value. While we may not know what changed, we can at least detect something manipulated the data.
The second intent is to compare the value of the instance on the server to the local copy. If the value is the same (on the server and locally) then the server has the up to date instance value.
public override ulong CalculateChecksum()