3,5/5. For an older audience then the format of the book might make you think. Yes it's a small book with a lot of illustrations, but the content is kind of dense and the informations about electricity, engineering and others things are well explain but at the same time clearly not intent for 5 year old of course... I would say maybe more around 9-10 years old, always hard to guess, but just don't get fooled by the format. If not and interesting book, nothing mind blowing but worth reading!