Whilst the ESL product has a self-contained scripting language, which is both powerful and efficient, there are occasions when your ESL application can benefit from the additional functionally that can be provided by calling a function or subroutine, that has been written in 'C'. For example; your application may need to perform a complex mathematical calculation, perform low level bit-wise logic or access third party products. All these requirements can be achieved by using 'C' routines, although it is not always necessary to write the 'C' code, as there is already a vast range of functions available within the Operating System, which can now be called directly from ESL.