  We review error estimation methods for co-simulation, in particular methods
that are applicable when the subsystems provide minimal interfaces. By this, we
mean that subsystems do not support rollback of time steps, do not output
derivatives, and do not provide any other information about their internals
other than the output variables that are required for coupling with other
subsystems. Such "black-box" subsystems are quite common in industrial
applications, and the ability to couple them and run large-system simulations
is one of the major attractions of the co-simulation paradigm. We also describe
how the resulting error indicators may be used to automatically control macro
time step sizes in order to strike a good balance between simulation speed and
accuracy. The various elements of the step size control algorithm are presented
in pseudocode so that readers may implement them and test them in their own
applications. We provide practicable advice on how to use error indicators to
judge the quality of a co-simulation, how to avoid common pitfalls, and how to
configure the step size control algorithm.
