I do agree with no sig, and a good point to start is either to get your hands on the Jeppesen/Oxford Mass & Balance ATPL manual or on the CAA booklet used for the actual ATPL exams - the thin yellow one, can't find it or remember what the CAP no. is! It's quite good for definitions.
In the same vein, it might be of use to follow that up with a Performance manual since a/c perf is dependent on mass and balance (along with other things such as atmospheric pressure, density alt, wind component, runway contamination, bleed air, etc).
Cheers
