Thank you very much for your interest in this survey! My name is Lisa Sonnleithner and I am a researcher at the CDL VaSiCS, LIT | Cyber-Physical Systems Lab (https://www.jku.at/en/lit-cyber-physical-systems-lab/) lead by Prof. Rick Rabiser and Prof. Alois Zoitl. My research focuses on IEC 61499 software architecture and software metrics. The questions in this survey aim to investigate the complexity of IEC 61131-3 Structured Text Function Blocks in IEC 61499.The goal of this survey is to assess developers' perception of complexity of IEC 61131-3 Structured Text Function Blocks in IEC 61499, i.e., how hard it is to understand a Function Block. We will use this information to assess which metric best represents that perception. This metric can then be implemented in any IEC 61499 development tool to provide meaningful feedback during the development process and help improve software quality. Therefore, by participating in this survey you not only help us with our research but you will also benefit from better tool support in the future!The Structured Text code used for the questions is mostly taken from real libraries.Completing this survey will only take around 10-15 minutes.