According to Babbage these scribbling books contain 'The first rough notions of the Difference and of the Analytical Engines were developed by sketches and calculations in Nine Volumes. Some of these became the basis of the drawings...' as well as an additional seven volumes '... others which contained materials belonging to the same subject. The dates are various and irregular'.

Volume I, known as 'The Tool Book', may not be the first chronological scribbling book, because of the dates. However as this volume is numbered 1 on the cover, as well as Vol. I by H.P. Babbage, the latter's numbering system has been retained.