The function sets the generation time of the given expression
value according to the current system time. The result is a value of the same
type as the expression.
Optional expression. Timestamp of the expression
value will be the current system time.
periodically re-calculated formula of an eval tag still returns the same
value, by default, the system does not assign a new time to this value,
unless it is changed. Using the function %NvtV is guaranteed, that the system will
assign a new time to every generation of such an unchanged value.