System dynamics , developed by J. W. Forrester in the 1960s, goes far beyond diagrams to analyse the behaviour of complex systems using qualitative and quantitative methods to model the dynamics of systems.
The models of Systems Dynamics go beyond those of sign graphs by providing mathematical fomulae to produce the value for the change at a node at at time t+1 based on all the input values at time t. This enables the values associated with each node to be computer through time as a computer simulation. We will say more about this in the context of the Science of Complex Systems in Week 2. Thus System Dynamics lies at the intersection between qualitative systems thinking and quantitative complex systems analysis.
Although systems diagrams can give deep insights into the behaviour of systems, they have their limitations. For example, by themselves complicated diagrams may not make it easy to understand large complex systems with many qualitative and quantitative elements, and many interacting feedback loops.
What do you think of the systems diagram above which depicts US military strategy in Afghanistan, which was criticised in the New York Times for its complexity?
 Jon Moynihan, ‘In using charts to grapple with complex situations we should support dynamic thinking and avoid the over-simplistic’, Letter published in The Times Newspaper, 3rd May 2010.