The term real-time is defined by FOLDOC  as following:
(Used to describe a system that must guarantee a response to an external event within a given time. )
Definition 1 puts the requirement of time more on the underlying operating system than the specific DCharts implementation. This is because the small upper limit of response time can only be guaranteed if the operating system supports it. For many common-purpose systems that model designers would most probably use, this guarantee is hard to achieve. For example, Linux only provides a very limited support for real-time computation; Windows and many other multi-tasking operating systems perform even more unsatisfactory within the real-time domain. To allow DCharts to be implemented on most systems and platforms, the real-time requirement cannot be formalized as strict as that in definition 1.
Definition 2 makes the real-time concept more general: the DCharts implementations provide real-time support for models within the extent of their capability. The model users watch the simulation/execution of the models and wait for them to respond.
The real-time concept is defined by Webopedia  in a similar way:
Definition 2 is useful for the understanding of the real-time required by DCharts. Similarly, the requirement of ``the same speed'' is not strict. DCharts implementations should provide this support as much as possible, given the restrictions of the operating systems that they are built for.
MSN Encarta  also defines the real-time concept, which is stricter than the real-time concept in DCharts:
In most cases, model designers may assume that 1 second elapsed in the model simulation or execution is approximately equal to 1 second in reality. Designers with time-critical requirements should turn to the documentation of specific DCharts implementations or operating systems to know whether they suit the need.