I am a retired Hospital and Medical Device R/D professional. I have been building model airplanes since I was 10 years old. I started flying RC airplanes in 1971 over 50 years ago. A need comes up periodically to understand aerodynamic theory as it applies to our small airplanes. I enjoy applying subsets of these equations to Excel spreadsheets. There are a few CG calculation programs on the web and a few methods are offered to calculate the CG and apply these answers to our models. Understanding mathematically how these methods and programs are derived is interesting to me. I believe the answers given should be similar (enough) and be based on the science of aerodynamics. Verifying these methods is a fun subset of my overall interests in this hobby.