This 5 point report discusses realisation and tuning of software based PID-controllers. The intended reader is an engineer that is interested in how a PID-controller is implemented and tuned with the AMIGO (Approximate M-constrained integral gain optimization) method. All mathematical reasoning is explained in detail step by step. The main purpose with this report is to gather knowledge from the reference sources, and clearly present this knowledge, so that it is accessible for engineers that work with PID-controllers. • How does a PID-controller function? • How can a PID-controller be implemented? • How is a PID-controller tuned?