During these private studies he recorded his observations and findings in a "Parliamentary Pocket Book". One writer states that "Thus the preparation of the Pocket-Book occupied him at intervals from his student days in George Wythe's law office to his years of retirement at Monticello after his two terms as President"(Wilbur Samuel Howell).
The 'Pocket Book' was useful in preparing the Manual of Parliamentary Practice. This work was undertaken by Jefferson to assist him in his role of presiding officer of the Senate. As Vice President (1797 to 1801) one of his key functions was that of President of the Senate (Veeps still play a role, though it is no longer as important as developing the rules of the Senate). Jefferson's Manual "is regarded by English Parliamentarians as the best statement of what the law of Parliament was at the time Jefferson wrote it" (Charles W Johnson). Although written for the Senate, it has been adopted by the House of Representatives. Rule XXIX 1 states "the rules of parliamentary practice comprised by Jefferson’s Manual shall govern the House in all cases to which they are applicable and in which they are not inconsistent with the Rules and orders of the House."
The Pocket Book, which is a fascinating read, is now available in 'Jefferson's Parliamentary Writings' (Princeton University Press)