Having an undergraduate background in maths from 45 years ago I was very pleased with the way the book reminded me and updated my understanding of the subject but, and it's a big but, the formulae have been reproduced at such a small size that for example the dot representing a time derivative is a single pixel. This and all the formulae cannot be easily read except in a very good light or by using the back light at maximum. (To forestall some obvious remarks, my eyesight is quite a lot better than standard and has been recently tested.) Some of the material requires concentration and puzzling over exactly which symbol has been used is a considerable distraction. Enlarging the font makes no difference, presumably because the formulae have been reproduced as images. I have not found any which could not have been reproduced at twice the size without upsetting the page layout. This is such a problem that I was tempted to assign two stars.