I enjoyed Longitude, but it would be better with even a few diagrams to explain some of the details of Harrison's clock making breakthroughs. I couldn't form a picture just from reading the text how his gridiron pendulum allowed for temperature changes, but I'm sure it could have been explained quite easily with a diagram and a reference to basic physics. The recent Horizon programme on the BBC made exactly the same mistake. Without more explanantion we are really being asked to take the author's word for it about how clever Harrison's clocks were. It's a good story though. One thing I'm still not sure about is how do you measure local noon on board ship any more accurately than you measure the moon's position. With a few more explanations this book could have been excellent.