The book seems to be in short supply at Amazon these days. We must have bought them out
But most of us start with the website and the calculator here
UpDayDownDay Diet(TM) Plan âEUR" How to Succeed
Have a read and believe it really is that simple. Eat what you want but stick to the calories. decide for yourself how many small calorie days your lifestyle can accommodate.
If you read round here you will find some doing 1 Down Day of about 500kcals, some do strictly alternating, most do 2 or 3 DDs a week and keep the weekend as normal eating days.... all sorts of variations. You may find your first couple of weeks 'jiggling' the days to find what pattern suits you best
Good luck and welcome to the wonderful, guilt free world of JUDDD.